Remove test debt: dead guards, discarded results, and unreferenced files (#5732)

* Run the README test case in JSON_FastTests jobs

The "README" test case was marked doctest::skip() when the tests
moved from Catch to doctest in 2019, where it replaced Catch's hidden
tag. It is not slow (17 assertions, about 0.00 s), but cmake/test.cmake
only passes --no-skip when JSON_FastTests is off, so the per-compiler
ci_test_*_cxxNN matrix, macOS, Windows Release/ARM, icpc, icpx and
nvhpc compiled the README examples without running them.

Drop the skip decorator so every job runs the case. Test-only change.

Part of #5713

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Remove stale clang ranges guards in unit-iterators2.cpp

The "algorithms" and "views" sections were guarded by clang/libstdc++
checks written for a clang 15 (04/2022) bug. The first guard's
condition contradicts its own comment: it skips clang+libc++ and
keeps clang+libstdc++. Both sections already sit inside
`#if JSON_HAS_RANGES`, which macro_scope.hpp excludes for the
toolchains these guards targeted, so the inner guards never let the
sections run on the platforms they meant to protect and are
redundant on the rest. Verified locally with Apple clang 21/libc++
and clang 16.0.6/libstdc++ 12 (Docker): both pass all 1355
assertions with the guards removed.

Part of #5713

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Fix copy-pasted CBOR half-float checks; enable stale encode checks

In the RFC 8949 Appendix A test case, the decode checks for
5.960464477539063e-8 (0xf9 0x00 0x01) and 0.00006103515625
(0xf9 0x04 0x00) were copy-pasted from the neighboring -4.0 example,
so those two half-float byte sequences were never actually decoded
and checked, and -4.0 was checked three times instead. The two
float32 encode checks for 100000.0 and 3.4028234663852886e+38 were
commented out before the writer supported emitting float32 and are
now verified to match byte for byte, so they are enabled. The
remaining commented-out half-precision to_cbor checks are collapsed
into a single explanatory comment, since the writer never emits
half-precision floats.

Part of #5713

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Assert on the result of STL container conversions in tests

The "object-like STL containers" and "array-like STL containers"
sections converted json values into std::map, unordered_map,
multimap, unordered_multimap, list, forward_list, array, valarray,
vector, deque, set and unordered_set and discarded the result, so
these ~60 conversions only proved that the code compiles and does
not throw; a conversion that dropped or reordered elements would
still pass. Bind each result and compare it against the expected
container. Also fix a copy-paste slip in the deque section
(`j2.get<std::deque<double>>()` instead of j3, so j3's doubles were
never converted to a deque), and remove the dead
`// CHECK(m5["one"] == "eins")` comments that referred to a variable
that did not exist by asserting the equivalent through the bound
result.

Part of #5713

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Deduplicate SaxCountdown and other test helpers across formats

SaxCountdown was copied byte-for-byte into six binary-format test
files (unit-cbor.cpp, unit-msgpack.cpp, unit-ubjson.cpp,
unit-bjdata.cpp, unit-bon8.cpp, unit-bson.cpp), about 370 redundant
lines. Move it into tests/src/sax_countdown.hpp (namespace utils,
alongside test_utils.hpp and round_trip_corpus.hpp) and include it
from all six.

trait_test_arg and the "value_in_range_of trait"
TEST_CASE_TEMPLATE_DEFINE were duplicated between unit-32bit.cpp and
unit-bjdata.cpp; the trait is a detail/meta trait, not specific to
either file. Move it into tests/src/value_in_range_of_test.hpp;
unit-32bit.cpp keeps its own include, since JSON_32bitTest=ONLY
builds only that file. Each file keeps its own
TEST_CASE_TEMPLATE_INVOKE list.

sax_no_exception and the "issue #2824" section were duplicated in
unit-regression2.cpp and unit-disabled_exceptions.cpp. Drop the copy
from unit-regression2.cpp; unit-disabled_exceptions.cpp already
covers the no-exceptions case that #2824 was about, and
ci_test_noexceptions reruns it.

No behavior change. Verified by building and running unit-cbor,
unit-msgpack, unit-ubjson, unit-bjdata, unit-bon8, unit-bson,
unit-32bit, unit-regression2 and unit-disabled_exceptions against
include/ (clang++ -std=c++11, ASan/UBSan where applicable); assertion
counts are unchanged from before the refactor.

Part of #5714

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Remove the unreferenced vendored libFuzzer

tests/thirdparty/Fuzzer (155 files, ~776 KB of vendored Apache-2.0
LLVM code from the 2016 OSS-Fuzz import) is not referenced by any
CMakeLists, Makefile or workflow: the fuzz drivers link against
-fsanitize=fuzzer or the repo's own
tests/src/fuzzer-driver_afl.cpp. Its vendored README only points at
llvm.org's own libFuzzer docs. Being dead code, it also adds noise
to the flawfinder code-scanning workflow, which scans the whole
tree. Remove the directory and its .reuse/dep5 entry.

Part of #5714

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Remove unreferenced 2016 benchmark and fuzz reports

tests/reports (1.6 MB) holds AFL status pages and plots from
2016-08-29 and 2016-10-02, and a nativejson-benchmark snapshot from
2016 with links to rawgit.com, which shut down in 2019. Nothing
references this directory: no doc, README section, script or
workflow points at it, and it describes a ten-years-old, pre-2.0
snapshot of the library.

Part of #5714

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Run the CBOR, MessagePack, BSON and BON8 round-trip invariants in CI

tests/src/round_trip_corpus.hpp exists so that the byte-stability
invariant the fuzzer drivers check also runs on a fixed corpus in CI,
instead of only at OSS-Fuzz. So far only the UBJSON and BJData drivers
had a matching unit test; the CBOR, MessagePack, BSON and BON8 drivers
assert the same invariant (assert(to_X(j2) == vec)) but nothing ran it
outside OSS-Fuzz.

Add "<FORMAT> round-trip invariants" test cases to unit-cbor.cpp,
unit-msgpack.cpp, unit-bson.cpp and unit-bon8.cpp, modeled on the
UBJSON case: seed j1 from the corpus (skipping values that do not
survive the format's own round trip, as the fuzzer drivers only ever
see values from_X() actually produced), then require from_X(to_X(j1))
not to throw and check to_X(j2) == to_X(j1). BSON only serializes
objects, so non-object corpus values are skipped. Update the comments
in round_trip_corpus.hpp and tests/fuzzing.md to name all six formats.

The stream-versus-contiguous check in the BON8 driver is left out, as
#5601 reworks it.

A local probe confirms no violations on the current corpus (CBOR 3849
checked, MessagePack 3909, BSON 2958, BON8 3841 - matching the counts
already recorded for this probe in the issue).

Closes #5714 item 1.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Fix fuzzer driver step lists to match the checks the code performs

The header comment of six of the seven binary-format fuzzer drivers
listed an invariant the code does not check: CBOR, MessagePack, BSON
and BON8 said "assert(j1 == j2)", but the code checks byte stability,
assert(to_X(j2) == vec). UBJSON and BJData still described the old
"assert(j1 == j2/j3/j4)" byte-exact check from before PR #5494 replaced
it with a use_size/use_type-aware round trip (UBJSON) and a
value-stability check (BJData); BJData's added paragraph already
explained the new check, but the step list above it did not.

Also remove a dead branch in fuzzer-parse_bson.cpp: from_bson() is
called with allow_exceptions = true, so it throws instead of returning
a discarded value, and the "if (j1.is_discarded()) return 0;" guard
could never trigger. Drop the unused <iostream> include from all seven
drivers and <sstream> from all but fuzzer-parse_bon8.cpp, which is the
only one that uses std::istringstream.

Overlaps #5601, which edits all seven drivers in the same hunks.

Closes #5714 item 4.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Silence the CMP0169 deprecation in cmake_fetch_content, fix stale guards

tests/cmake_fetch_content/project calls the single-argument
FetchContent_Populate(json) after FetchContent_Declare(), which CMake
3.30 deprecated as CMP0169. Since the project declares
cmake_minimum_required(VERSION 3.11...3.14), the policy stays unset,
so every configure with a current CMake prints the deprecation
warning. The test is kept on purpose: it is the only coverage of the
FetchContent_Populate + add_subdirectory pattern for CMake 3.11-3.13
users, which the docs still describe as supported. Explicitly set
CMP0169 to OLD, with a comment explaining why.

Also fix two stale version guards:
- tests/cmake_fetch_content/CMakeLists.txt guarded the test with
  VERSION_GREATER "3.11.0", which is dead now that tests/CMakeLists.txt
  requires CMake 3.13.
- tests/cmake_fetch_content2/CMakeLists.txt guarded with
  VERSION_GREATER "3.14.0", which skips exactly 3.14.0, the first
  version with FetchContent_MakeAvailable. Change it to
  VERSION_GREATER_EQUAL "3.14".

Verified locally: `ctest -R cmake_fetch_content` passes with CMake
4.1, and the CMP0169 deprecation warning that appeared before this
change is gone.

Closes #5714 item 5.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Make the CMake integration-test wrappers consistent

The six tests/cmake_* integration-test wrappers had drifted:

- Only cmake_import and cmake_import_minver forwarded
  -A "${CMAKE_GENERATOR_PLATFORM}" to the inner configure, and none
  forwarded -T "${CMAKE_GENERATOR_TOOLSET}". The Windows workflow
  configures the outer build with -A Win32 -T ClangCL, so without
  forwarding, the inner projects of cmake_add_subdirectory,
  cmake_fetch_content, cmake_fetch_content2 and
  cmake_target_include_directories built with the generator defaults
  instead of matching the outer build's platform and toolset. Forward
  both consistently from all six wrappers.
- cmake_fetch_content and cmake_fetch_content2 passed
  -Dnlohmann_json_source to their inner projects, which never read it
  (CMake warns "manually-specified variables were not used"); the
  inner projects fetch their own copy of the library instead. Drop it.
- tests/CMakeLists.txt set JSON_FORCED_GLOBAL_COMPILE_OPTIONS from the
  matching environment variable but never read the cache variable
  again; the lines right below it read $ENV{JSON_FORCED_GLOBAL_COMPILE_OPTIONS}
  directly, like the LINK_OPTIONS counterpart already does. Remove the
  dead set().

This changes which platform and toolset the Win32 and ClangCL CI jobs
build the four newly-forwarding wrappers' inner projects with, which
may surface new failures there; CI has to confirm those jobs.

Verified locally with Ninja (empty -A ""/-T "" is accepted): all 12
cmake_* tests still pass, and the inner fetch_content configures no
longer warn about the unused variable.

Closes #5714 item 6.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Turn the #972 fifo_map regression test into a real test

The #972 regression test in unit-regression1.cpp only built a
my_json array from a string literal (the original crash) and had no
CHECK, so the fifo_map object type it exists to demonstrate was never
exercised. Meanwhile the docs recommend fifo_map for keeping object
keys in insertion order (object_order.md, template_parameters.md),
and nothing tested that recommendation.

Extend the section: after the original array assignment, parse an
object with my_json::parse() (not via the "..."_json UDL, which
returns a plain nlohmann::json and would exercise the cross-basic_json
conversion constructor instead of the parser's own key insertion -
and, as tried locally, does not keep fifo order for this stateful
comparator) and check that dump() keeps insertion order, and that it
survives erase() and inserting a new key.

Also narrow thirdparty/fifo_map off the include path of every other
test-* target: it was a PUBLIC include directory of test_main, even
though unit-regression1.cpp is its only user. Add a small
fifo_map_include INTERFACE library with that include directory and
attach it to test-regression1 only via json_test_set_test_options().

Verified locally (test-regression1_cpp11, default build and
-fsanitize=address,undefined): the new checks pass; `git grep fifo_map
tests` still only finds unit-regression1.cpp and the vendored header.

Closes #5714 item 7.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Document the vendored doctest.h patch; fix stale doctest_compatibility.h comments

tests/thirdparty/doctest/doctest.h is doctest 2.4.12, imported in
#4771. Two weeks later, #4801 hand-edited translateActiveException()
to declare "String res;" inside the translator loop instead of before
it, so a translator that does not match does not leave a previous
translator's result in "res" for the next iteration to see. Nothing
recorded this, so re-vendoring doctest.h from upstream would silently
drop the fix. Add a comment at the patched site naming the version,
the PR and the reason, so a future re-vendor knows to re-apply it.

Also fix two stale comments in doctest_compatibility.h:
- The DOCTEST_THREAD_LOCAL comment referenced Xcode 6/7, which is no
  longer supported; reword it to explain why the define must stay
  regardless (it keeps doctest's own thread_local usage out of the way
  of the same Clang/MinGW crash that JSON_NO_THREAD_LOCAL works around
  in the library, see ci_test_no_thread_local).
- The <iosfwd> include's comment justified it with tests that define
  "private" as "public"; no test under tests/src does that any more
  (removed by #2352). Reword the comment instead of dropping the
  include, since confirming it is safe to drop needs the full CI
  matrix including MSVC 2015+.

Verified locally that tests/src/unit-readme.cpp still builds and
passes 17/17 with these headers.

Closes #5714 item 9.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

* Stop compiling unit-wstring.cpp out entirely on classic ICC

tests/src/unit-wstring.cpp wrapped the whole file in
#ifndef __INTEL_COMPILER, with the comment "ICPC errors out on
multibyte character sequences in source files". The ci_icpc job
(intel/oneapi-hpckit:2023.2.1) still exists, so that job ran none of
the wstring/u16string/u32string input adapter tests, including the
malformed-input checks #5704 (open) extends.

Only 9 lines contained non-ASCII bytes: the three *_is_utf16()/
*_is_utf32() probe functions, and three std::wstring/u16string/
u32string literals plus their narrow-string dump() expectations.
Rewrite all of them with \u/\U escapes in the wide/u16/u32 literals
and \x escapes (split into separate string-literal tokens so a
following byte is never read as part of the same hex escape, e.g.
"\xE1\x83\x85" "a") in the narrow ones. Remove the
#ifndef __INTEL_COMPILER/#endif guard along with it.

The *_is_utf16()/*_is_utf32() probes compared a raw multibyte literal
against an escape-based one to detect a compiler that misreads the
source file's encoding; with no raw literals left to misread, the
comparison is now tautological, so drop the probes and the "if"
guards around each SECTION's body instead of leaving them in as dead
checks.

The same non-ASCII-in-source-and-in-a-narrow-comparison pattern
existed once more in unit-deserialization.cpp's "Using _json with
char8_t literals #4945" test: a raw emoji character in a u8R"(...)"
literal, guarded by a check_utf8() that returned false for ICC (same
reason) and for Windows without the active UTF-8 code page. Rewrite
the literal with a \U escape and compare it against a \x-escaped
expectation instead of a second raw literal, and drop check_utf8()
and the now-unused <windows.h> include along with the guard.

Verified locally (clang, -std=c++11 and -std=c++20,
-fsanitize=address,undefined, and a plain build): test-wstring keeps
18/18 assertions and unit-deserialization keeps 466/466 (c++11) and
477/477 (c++20) assertions, matching this branch before the change
exactly - no coverage was gained or lost, only the source-encoding
dependency was removed. ci_icpc has to confirm classic ICC actually
builds and passes test-wstring now; if it does not, that is a real
finding, not a reason to restore the guard.

Overlaps #5704 (open), which edits unit-wstring.cpp inside the
previously-guarded region (an include near the top, checks in the
invalid-string sections, and a new section at the end).

Closes #5713 item 5.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

---------

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

tests/src/fuzzer-parse_bjdata.cpp

@@ -11,15 +11,15 @@ This file implements a parser test suitable for fuzz testing. Given a byte
 array data, it performs the following steps:
 
 - j1 = from_bjdata(data)
-- vec = to_bjdata(j1)
-- j2 = from_bjdata(vec)
-- assert(j1 == j2)
-- vec2 = to_bjdata(j1, use_size = true, use_type = false)
-- j3 = from_bjdata(vec2)
-- assert(j1 == j3)
-- vec3 = to_bjdata(j1, use_size = true, use_type = true)
-- j4 = from_bjdata(vec3)
-- assert(j1 == j4)
+- vec2 = to_bjdata(j1, use_size = false, use_type = false)
+- vec3 = to_bjdata(j1, use_size = true, use_type = false)
+- vec4 = to_bjdata(j1, use_size = true, use_type = true)
+- j2 = from_bjdata(vec2)
+- j3 = from_bjdata(vec3)
+- j4 = from_bjdata(vec4)
+- assert(from_bjdata(to_bjdata(j2, use_size = false, use_type = false)) is value-stable with j2)
+- assert(from_bjdata(to_bjdata(j3, use_size = true, use_type = false)) is value-stable with j3)
+- assert(from_bjdata(to_bjdata(j4, use_size = true, use_type = true)) is value-stable with j4)
 
 Re-serializing j2/j3/j4 with the same use_size/use_type settings is checked
 for value-stability rather than byte-exact stability: from_bjdata(to_bjdata(j2))
@@ -50,8 +50,6 @@ drivers.
 */
 
 #include <cassert>
-#include <iostream>
-#include <sstream>
 #include <nlohmann/json.hpp>
 
 // the round-trip checks below are assertions; NDEBUG would compile them away

tests/src/fuzzer-parse_bon8.cpp

@@ -13,7 +13,7 @@ array data, it performs the following steps:
 - j1 = from_bon8(data)
 - vec = to_bon8(j1)
 - j2 = from_bon8(vec)
-- assert(j1 == j2)
+- assert(to_bon8(j2) == vec)
 
 It also checks that reading the data from a stream, which reads strings byte by
 byte, gives the same value or error as reading it from contiguous memory, which
@@ -24,7 +24,6 @@ drivers.
 */
 
 #include <cassert>
-#include <iostream>
 #include <sstream>
 #include <nlohmann/json.hpp>
 

tests/src/fuzzer-parse_bson.cpp

@@ -13,15 +13,13 @@ array data, it performs the following steps:
 - j1 = from_bson(data)
 - vec = to_bson(j1)
 - j2 = from_bson(vec)
-- assert(j1 == j2)
+- assert(to_bson(j2) == vec)
 
 The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */
 
 #include <cassert>
-#include <iostream>
-#include <sstream>
 #include <nlohmann/json.hpp>
 
 // the round-trip checks below are assertions; NDEBUG would compile them away
@@ -40,11 +38,6 @@ extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size)
         std::vector<uint8_t> const vec1(data, data + size);
         json const j1 = json::from_bson(vec1);
 
-        if (j1.is_discarded())
-        {
-            return 0;
-        }
-
         try
         {
             // step 2: round trip

tests/src/fuzzer-parse_cbor.cpp

@@ -13,15 +13,13 @@ array data, it performs the following steps:
 - j1 = from_cbor(data)
 - vec = to_cbor(j1)
 - j2 = from_cbor(vec)
-- assert(j1 == j2)
+- assert(to_cbor(j2) == vec)
 
 The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */
 
 #include <cassert>
-#include <iostream>
-#include <sstream>
 #include <nlohmann/json.hpp>
 
 // the round-trip checks below are assertions; NDEBUG would compile them away

tests/src/fuzzer-parse_json.cpp

@@ -21,8 +21,6 @@ drivers.
 */
 
 #include <cassert>
-#include <iostream>
-#include <sstream>
 #include <nlohmann/json.hpp>
 
 // the round-trip checks below are assertions; NDEBUG would compile them away

tests/src/fuzzer-parse_msgpack.cpp

@@ -13,15 +13,13 @@ array data, it performs the following steps:
 - j1 = from_msgpack(data)
 - vec = to_msgpack(j1)
 - j2 = from_msgpack(vec)
-- assert(j1 == j2)
+- assert(to_msgpack(j2) == vec)
 
 The provided function `LLVMFuzzerTestOneInput` can be used in different fuzzer
 drivers.
 */
 
 #include <cassert>
-#include <iostream>
-#include <sstream>
 #include <nlohmann/json.hpp>
 
 // the round-trip checks below are assertions; NDEBUG would compile them away

tests/src/fuzzer-parse_ubjson.cpp

@@ -11,15 +11,15 @@ This file implements a parser test suitable for fuzz testing. Given a byte
 array data, it performs the following steps:
 
 - j1 = from_ubjson(data)
-- vec = to_ubjson(j1)
-- j2 = from_ubjson(vec)
-- assert(j1 == j2)
-- vec2 = to_ubjson(j1, use_size = true, use_type = false)
-- j3 = from_ubjson(vec2)
-- assert(j1 == j3)
-- vec3 = to_ubjson(j1, use_size = true, use_type = true)
-- j4 = from_ubjson(vec3)
-- assert(j1 == j4)
+- vec2 = to_ubjson(j1, use_size = false, use_type = false)
+- vec3 = to_ubjson(j1, use_size = true, use_type = false)
+- vec4 = to_ubjson(j1, use_size = true, use_type = true)
+- j2 = from_ubjson(vec2)
+- j3 = from_ubjson(vec3)
+- j4 = from_ubjson(vec4)
+- assert(to_ubjson(j2, use_size = false, use_type = false) == vec2)
+- assert(to_ubjson(j3, use_size = true, use_type = false) == vec3)
+- assert(to_ubjson(j4, use_size = true, use_type = true) == vec4)
 
 The unit tests run the same checks on a fixed corpus (see the "UBJSON round-trip
 invariants" test case), so keep both in sync.
@@ -29,8 +29,6 @@ drivers.
 */
 
 #include <cassert>
-#include <iostream>
-#include <sstream>
 #include <nlohmann/json.hpp>
 
 // the round-trip checks below are assertions; NDEBUG would compile them away

tests/src/round_trip_corpus.hpp

@@ -19,13 +19,14 @@
 
 #include <nlohmann/json.hpp>
 
-// Values for the round-trip property tests of the UBJSON and BJData writers.
+// Values for the round-trip property tests of the binary format writers
+// (BJData, BON8, BSON, CBOR, MessagePack and UBJSON).
 //
-// The fuzzer drivers (tests/src/fuzzer-parse_ubjson.cpp and
-// fuzzer-parse_bjdata.cpp) check that anything the library parses can be
-// serialized, parsed back, and serialized again without loss. Those checks
-// only run at OSS-Fuzz, so a regression used to surface days later as an
-// external report. The unit tests run the same checks on this corpus in CI.
+// The fuzzer drivers (tests/src/fuzzer-parse_*.cpp) check that anything the
+// library parses can be serialized, parsed back, and serialized again
+// without loss. Those checks only run at OSS-Fuzz, so a regression used to
+// surface days later as an external report. The unit tests run the same
+// checks on this corpus in CI.
 //
 // The corpus is deterministic: std::mt19937's output sequence is fixed by
 // the standard, and it is used directly rather than through a distribution

tests/src/sax_countdown.hpp

@@ -0,0 +1,99 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+#include <string>
+#include <vector>
+
+#include <nlohmann/json.hpp>
+
+namespace utils
+{
+/// a SAX event consumer that stops accepting events after a fixed count,
+/// used by the binary-format tests to check behavior when the SAX consumer
+/// rejects an event partway through parsing
+class SaxCountdown
+{
+  public:
+    using json = nlohmann::json;
+
+    explicit SaxCountdown(const int count) : events_left(count)
+    {}
+
+    bool null()
+    {
+        return events_left-- > 0;
+    }
+
+    bool boolean(bool /*unused*/)
+    {
+        return events_left-- > 0;
+    }
+
+    bool number_integer(json::number_integer_t /*unused*/)
+    {
+        return events_left-- > 0;
+    }
+
+    bool number_unsigned(json::number_unsigned_t /*unused*/)
+    {
+        return events_left-- > 0;
+    }
+
+    bool number_float(json::number_float_t /*unused*/, const std::string& /*unused*/)
+    {
+        return events_left-- > 0;
+    }
+
+    bool string(std::string& /*unused*/)
+    {
+        return events_left-- > 0;
+    }
+
+    bool binary(std::vector<std::uint8_t>& /*unused*/)
+    {
+        return events_left-- > 0;
+    }
+
+    bool start_object(std::size_t /*unused*/)
+    {
+        return events_left-- > 0;
+    }
+
+    bool key(std::string& /*unused*/)
+    {
+        return events_left-- > 0;
+    }
+
+    bool end_object()
+    {
+        return events_left-- > 0;
+    }
+
+    bool start_array(std::size_t /*unused*/)
+    {
+        return events_left-- > 0;
+    }
+
+    bool end_array()
+    {
+        return events_left-- > 0;
+    }
+
+    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/, const json::exception& /*unused*/) // NOLINT(readability-convert-member-functions-to-static)
+    {
+        return false;
+    }
+
+  private:
+    int events_left = 0;
+};
+} // namespace utils

tests/src/unit-32bit.cpp

@@ -12,80 +12,11 @@
 using nlohmann::json;
 
 #include <climits> // SIZE_MAX
-#include <limits> // numeric_limits
 
-template <typename OfType, typename T, bool MinInRange, bool MaxInRange>
-struct trait_test_arg
-{
-    using of_type = OfType;
-    using type = T;
-    static constexpr bool min_in_range = MinInRange;
-    static constexpr bool max_in_range = MaxInRange;
-};
-
-TEST_CASE_TEMPLATE_DEFINE("value_in_range_of trait", T, value_in_range_of_test) // NOLINT(readability-math-missing-parentheses)
-{
-    using nlohmann::detail::value_in_range_of;
-
-    using of_type = typename T::of_type;
-    using type = typename T::type;
-    constexpr bool min_in_range = T::min_in_range;
-    constexpr bool max_in_range = T::max_in_range;
-
-    type const val_min = std::numeric_limits<type>::min();
-    type const val_min2 = val_min + 1;
-    type const val_max = std::numeric_limits<type>::max();
-    type const val_max2 = val_max - 1;
-
-    REQUIRE(CHAR_BIT == 8);
-
-    std::string of_type_str;
-    if (std::is_unsigned<of_type>::value)
-    {
-        of_type_str += "u";
-    }
-    of_type_str += "int";
-    of_type_str += std::to_string(sizeof(of_type) * 8);
-
-    INFO("of_type := ", of_type_str);
-
-    std::string type_str;
-    if (std::is_unsigned<type>::value)
-    {
-        type_str += "u";
-    }
-    type_str += "int";
-    type_str += std::to_string(sizeof(type) * 8);
-
-    INFO("type := ", type_str);
-
-    CAPTURE(val_min);
-    CAPTURE(min_in_range);
-    CAPTURE(val_max);
-    CAPTURE(max_in_range);
-
-    if (min_in_range)
-    {
-        CHECK(value_in_range_of<of_type>(val_min));
-        CHECK(value_in_range_of<of_type>(val_min2));
-    }
-    else
-    {
-        CHECK_FALSE(value_in_range_of<of_type>(val_min));
-        CHECK_FALSE(value_in_range_of<of_type>(val_min2));
-    }
-
-    if (max_in_range)
-    {
-        CHECK(value_in_range_of<of_type>(val_max));
-        CHECK(value_in_range_of<of_type>(val_max2));
-    }
-    else
-    {
-        CHECK_FALSE(value_in_range_of<of_type>(val_max));
-        CHECK_FALSE(value_in_range_of<of_type>(val_max2));
-    }
-}
+// JSON_32bitTest=ONLY builds only this file, so it must keep its own
+// include of the shared trait/TEST_CASE_TEMPLATE_DEFINE rather than relying
+// on unit-bjdata.cpp to provide it
+#include "value_in_range_of_test.hpp"
 
 TEST_CASE("32bit")
 {

tests/src/unit-bjdata.cpp

@@ -21,158 +21,13 @@ using nlohmann::json;
 #include "make_test_data_available.hpp"
 #include "round_trip_corpus.hpp"
 #include "test_utils.hpp"
+#include "sax_countdown.hpp"
+using utils::SaxCountdown;
 
-namespace
-{
-class SaxCountdown
-{
-  public:
-    explicit SaxCountdown(const int count) : events_left(count)
-    {}
 
-    bool null()
-    {
-        return events_left-- > 0;
-    }
-
-    bool boolean(bool /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_integer(json::number_integer_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_unsigned(json::number_unsigned_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_float(json::number_float_t /*unused*/, const std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool string(std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool binary(std::vector<std::uint8_t>& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool start_object(std::size_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool key(std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool end_object()
-    {
-        return events_left-- > 0;
-    }
-
-    bool start_array(std::size_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool end_array()
-    {
-        return events_left-- > 0;
-    }
-
-    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/, const json::exception& /*unused*/) // NOLINT(readability-convert-member-functions-to-static)
-    {
-        return false;
-    }
-
-  private:
-    int events_left = 0;
-};
-} // namespace
-
-// at some point in the future, a unit test dedicated to type traits might be a good idea
-template <typename OfType, typename T, bool MinInRange, bool MaxInRange>
-struct trait_test_arg
-{
-    using of_type = OfType;
-    using type = T;
-    static constexpr bool min_in_range = MinInRange;
-    static constexpr bool max_in_range = MaxInRange;
-};
-
-TEST_CASE_TEMPLATE_DEFINE("value_in_range_of trait", T, value_in_range_of_test) // NOLINT(readability-math-missing-parentheses)
-{
-    using nlohmann::detail::value_in_range_of;
-
-    using of_type = typename T::of_type;
-    using type = typename T::type;
-    constexpr bool min_in_range = T::min_in_range;
-    constexpr bool max_in_range = T::max_in_range;
-
-    type const val_min = std::numeric_limits<type>::min();
-    type const val_min2 = val_min + 1;
-    type const val_max = std::numeric_limits<type>::max();
-    type const val_max2 = val_max - 1;
-
-    REQUIRE(CHAR_BIT == 8);
-
-    std::string of_type_str;
-    if (std::is_unsigned<of_type>::value)
-    {
-        of_type_str += "u";
-    }
-    of_type_str += "int";
-    of_type_str += std::to_string(sizeof(of_type) * 8);
-
-    INFO("of_type := ", of_type_str);
-
-    std::string type_str;
-    if (std::is_unsigned<type>::value)
-    {
-        type_str += "u";
-    }
-    type_str += "int";
-    type_str += std::to_string(sizeof(type) * 8);
-
-    INFO("type := ", type_str);
-
-    CAPTURE(val_min);
-    CAPTURE(min_in_range);
-    CAPTURE(val_max);
-    CAPTURE(max_in_range);
-
-    if (min_in_range)
-    {
-        CHECK(value_in_range_of<of_type>(val_min));
-        CHECK(value_in_range_of<of_type>(val_min2));
-    }
-    else
-    {
-        CHECK_FALSE(value_in_range_of<of_type>(val_min));
-        CHECK_FALSE(value_in_range_of<of_type>(val_min2));
-    }
-
-    if (max_in_range)
-    {
-        CHECK(value_in_range_of<of_type>(val_max));
-        CHECK(value_in_range_of<of_type>(val_max2));
-    }
-    else
-    {
-        CHECK_FALSE(value_in_range_of<of_type>(val_max));
-        CHECK_FALSE(value_in_range_of<of_type>(val_max2));
-    }
-}
+// trait_test_arg and the "value_in_range_of trait" TEST_CASE_TEMPLATE_DEFINE
+// are shared with unit-32bit.cpp
+#include "value_in_range_of_test.hpp"
 
 // NOLINTNEXTLINE(bugprone-throwing-static-initialization)
 TEST_CASE_TEMPLATE_INVOKE(value_in_range_of_test, \

tests/src/unit-bon8.cpp

@@ -21,85 +21,13 @@ using nlohmann::json;
 #include <string>
 #include <vector>
 #include "make_test_data_available.hpp"
+#include "round_trip_corpus.hpp"
 #include "test_utils.hpp"
+#include "sax_countdown.hpp"
+using utils::SaxCountdown;
 
 namespace
 {
-class SaxCountdown
-{
-  public:
-    explicit SaxCountdown(const int count) : events_left(count)
-    {}
-
-    bool null()
-    {
-        return events_left-- > 0;
-    }
-
-    bool boolean(bool /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_integer(json::number_integer_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_unsigned(json::number_unsigned_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_float(json::number_float_t /*unused*/, const std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool string(std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool binary(std::vector<std::uint8_t>& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool start_object(std::size_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool key(std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool end_object()
-    {
-        return events_left-- > 0;
-    }
-
-    bool start_array(std::size_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool end_array()
-    {
-        return events_left-- > 0;
-    }
-
-    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/, const json::exception& /*unused*/) // NOLINT(readability-convert-member-functions-to-static)
-    {
-        return false;
-    }
-
-  private:
-    int events_left = 0;
-};
-
 using bytes = std::vector<std::uint8_t>;
 
 /// @return the string with the given bytes
@@ -817,6 +745,39 @@ TEST_CASE("Parse BON8 directly from a file using iterator and sentinel")
     CHECK((parsed.is_object() || parsed.is_array()));
 }
 
+TEST_CASE("BON8 round-trip invariants")
+{
+    // This checks what the parse_bon8_fuzzer driver checks (see
+    // tests/src/fuzzer-parse_bon8.cpp), so that a regression shows up in CI
+    // rather than as an OSS-Fuzz report: anything from_bon8() returns (j1)
+    // can be serialized, parsed back (j2), and serialized again to reproduce
+    // the exact bytes. The stream-versus-contiguous input check the driver
+    // also performs is not covered here (see #5601).
+    for (const auto& j0 : utils::round_trip_corpus::values())
+    {
+        json j1;
+        try
+        {
+            // turn the corpus value into a value as from_bon8() returns it
+            j1 = json::from_bon8(json::to_bon8(j0));
+        }
+        catch (const json::exception&)
+        {
+            // BON8 cannot represent an unsigned integer above INT64_MAX, and
+            // the fuzzer driver only ever sees values from_bon8() actually
+            // produced, so skip such corpus values here, too
+            continue;
+        }
+
+        INFO("j1 = " << j1.dump());
+        const std::vector<std::uint8_t> vec = json::to_bon8(j1);
+        json j2;
+        // anything the library writes must be parsable by the library
+        REQUIRE_NOTHROW(j2 = json::from_bon8(vec));
+        CHECK(json::to_bon8(j2) == vec);
+    }
+}
+
 TEST_CASE("BON8 roundtrips" * doctest::skip())
 {
     SECTION("input from HikoGUI")

tests/src/unit-bson.cpp

@@ -17,7 +17,10 @@ using nlohmann::json;
 #include <sstream>
 #include <vector>
 #include "make_test_data_available.hpp"
+#include "round_trip_corpus.hpp"
 #include "test_utils.hpp"
+#include "sax_countdown.hpp"
+using utils::SaxCountdown;
 
 namespace
 {
@@ -861,83 +864,6 @@ TEST_CASE("BSON input/output_adapters")
     }
 }
 
-namespace
-{
-class SaxCountdown
-{
-  public:
-    explicit SaxCountdown(const int count) : events_left(count)
-    {}
-
-    bool null()
-    {
-        return events_left-- > 0;
-    }
-
-    bool boolean(bool /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_integer(json::number_integer_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_unsigned(json::number_unsigned_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_float(json::number_float_t /*unused*/, const std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool string(std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool binary(std::vector<std::uint8_t>& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool start_object(std::size_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool key(std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool end_object()
-    {
-        return events_left-- > 0;
-    }
-
-    bool start_array(std::size_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool end_array()
-    {
-        return events_left-- > 0;
-    }
-
-    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/, const json::exception& /*unused*/) // NOLINT(readability-convert-member-functions-to-static)
-    {
-        return false;
-    }
-
-  private:
-    int events_left = 0;
-};
-} // namespace
 
 TEST_CASE("Incomplete BSON Input")
 {
@@ -1692,6 +1618,44 @@ TEST_CASE("Parse BSON directly from a file using iterator and sentinel")
     CHECK(parsed == expected);
 }
 
+TEST_CASE("BSON round-trip invariants")
+{
+    // This checks what the parse_bson_fuzzer driver checks (see
+    // tests/src/fuzzer-parse_bson.cpp), so that a regression shows up in CI
+    // rather than as an OSS-Fuzz report: anything from_bson() returns (j1)
+    // can be serialized, parsed back (j2), and serialized again to reproduce
+    // the exact bytes. BSON only serializes objects, so non-object corpus
+    // values are skipped.
+    for (const auto& j0 : utils::round_trip_corpus::values())
+    {
+        if (!j0.is_object())
+        {
+            continue;
+        }
+
+        json j1;
+        try
+        {
+            // turn the corpus value into a value as from_bson() returns it
+            j1 = json::from_bson(json::to_bson(j0));
+        }
+        catch (const json::exception&)
+        {
+            // the fuzzer driver only ever sees values from_bson() actually
+            // produced, so skip corpus values that do not survive the
+            // round trip here, too
+            continue;
+        }
+
+        INFO("j1 = " << j1.dump());
+        const std::vector<std::uint8_t> vec = json::to_bson(j1);
+        json j2;
+        // anything the library writes must be parsable by the library
+        REQUIRE_NOTHROW(j2 = json::from_bson(vec));
+        CHECK(json::to_bson(j2) == vec);
+    }
+}
+
 TEST_CASE("BSON roundtrips" * doctest::skip())
 {
     SECTION("reference files")

tests/src/unit-cbor.cpp

@@ -18,85 +18,11 @@ using nlohmann::json;
 #include <list>
 #include <set>
 #include "make_test_data_available.hpp"
+#include "round_trip_corpus.hpp"
 #include "test_utils.hpp"
+#include "sax_countdown.hpp"
+using utils::SaxCountdown;
 
-namespace
-{
-class SaxCountdown
-{
-  public:
-    explicit SaxCountdown(const int count) : events_left(count)
-    {}
-
-    bool null()
-    {
-        return events_left-- > 0;
-    }
-
-    bool boolean(bool /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_integer(json::number_integer_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_unsigned(json::number_unsigned_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_float(json::number_float_t /*unused*/, const std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool string(std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool binary(std::vector<std::uint8_t>& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool start_object(std::size_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool key(std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool end_object()
-    {
-        return events_left-- > 0;
-    }
-
-    bool start_array(std::size_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool end_array()
-    {
-        return events_left-- > 0;
-    }
-
-    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/, const json::exception& /*unused*/) // NOLINT(readability-convert-member-functions-to-static)
-    {
-        return false;
-    }
-
-  private:
-    int events_left = 0;
-};
-} // namespace
 
 TEST_CASE("CBOR")
 {
@@ -2415,6 +2341,39 @@ TEST_CASE("issue #5405 - array reserve for definite-length CBOR arrays")
     }
 }
 
+TEST_CASE("CBOR round-trip invariants")
+{
+    // This checks what the parse_cbor_fuzzer driver checks (see
+    // tests/src/fuzzer-parse_cbor.cpp), so that a regression shows up in CI
+    // rather than as an OSS-Fuzz report: anything from_cbor() returns (j1)
+    // can be serialized, parsed back (j2), and serialized again to reproduce
+    // the exact bytes.
+    for (const auto& j0 : utils::round_trip_corpus::values())
+    {
+        json j1;
+        try
+        {
+            // turn the corpus value into a value as from_cbor() returns it
+            j1 = json::from_cbor(json::to_cbor(j0));
+        }
+        catch (const json::exception&)
+        {
+            // not every corpus value survives a CBOR round trip (e.g., a
+            // binary subtype is written with a tag the default tag handler
+            // then rejects); the fuzzer driver only ever sees values
+            // from_cbor() actually produced, so skip those here, too
+            continue;
+        }
+
+        INFO("j1 = " << j1.dump());
+        const std::vector<std::uint8_t> vec = json::to_cbor(j1);
+        json j2;
+        // anything the library writes must be parsable by the library
+        REQUIRE_NOTHROW(j2 = json::from_cbor(vec));
+        CHECK(json::to_cbor(j2) == vec);
+    }
+}
+
 TEST_CASE("CBOR roundtrips" * doctest::skip())
 {
     SECTION("input from flynn")
@@ -2774,33 +2733,21 @@ TEST_CASE("examples from RFC 8949 Appendix A")
         CHECK(json::to_cbor(json::parse("1.1")) == std::vector<uint8_t>({0xfb, 0x3f, 0xf1, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9a}));
         CHECK(json::parse("1.1") == json::from_cbor(std::vector<uint8_t>({0xfb, 0x3f, 0xf1, 0x99, 0x99, 0x99, 0x99, 0x99, 0x9a})));
 
-        // half-precision float
-        //CHECK(json::to_cbor(json::parse("1.5")) == std::vector<uint8_t>({0xf9, 0x3e, 0x00}));
+        // the writer never emits half-precision floats, so these can only be decoded, not encoded
         CHECK(json::parse("1.5") == json::from_cbor(std::vector<uint8_t>({0xf9, 0x3e, 0x00})));
-
-        // half-precision float
-        //CHECK(json::to_cbor(json::parse("65504.0")) == std::vector<uint8_t>({0xf9, 0x7b, 0xff}));
         CHECK(json::parse("65504.0") == json::from_cbor(std::vector<uint8_t>({0xf9, 0x7b, 0xff})));
 
-        //CHECK(json::to_cbor(json::parse("100000.0")) == std::vector<uint8_t>({0xfa, 0x47, 0xc3, 0x50, 0x00}));
+        CHECK(json::to_cbor(json::parse("100000.0")) == std::vector<uint8_t>({0xfa, 0x47, 0xc3, 0x50, 0x00}));
         CHECK(json::parse("100000.0") == json::from_cbor(std::vector<uint8_t>({0xfa, 0x47, 0xc3, 0x50, 0x00})));
 
-        //CHECK(json::to_cbor(json::parse("3.4028234663852886e+38")) == std::vector<uint8_t>({0xfa, 0x7f, 0x7f, 0xff, 0xff}));
+        CHECK(json::to_cbor(json::parse("3.4028234663852886e+38")) == std::vector<uint8_t>({0xfa, 0x7f, 0x7f, 0xff, 0xff}));
         CHECK(json::parse("3.4028234663852886e+38") == json::from_cbor(std::vector<uint8_t>({0xfa, 0x7f, 0x7f, 0xff, 0xff})));
 
         CHECK(json::to_cbor(json::parse("1.0e+300")) == std::vector<uint8_t>({0xfb, 0x7e, 0x37, 0xe4, 0x3c, 0x88, 0x00, 0x75, 0x9c}));
         CHECK(json::parse("1.0e+300") == json::from_cbor(std::vector<uint8_t>({0xfb, 0x7e, 0x37, 0xe4, 0x3c, 0x88, 0x00, 0x75, 0x9c})));
 
-        // half-precision float
-        //CHECK(json::to_cbor(json::parse("5.960464477539063e-8")) == std::vector<uint8_t>({0xf9, 0x00, 0x01}));
-        CHECK(json::parse("-4.0") == json::from_cbor(std::vector<uint8_t>({0xf9, 0xc4, 0x00})));
-
-        // half-precision float
-        //CHECK(json::to_cbor(json::parse("0.00006103515625")) == std::vector<uint8_t>({0xf9, 0x04, 0x00}));
-        CHECK(json::parse("-4.0") == json::from_cbor(std::vector<uint8_t>({0xf9, 0xc4, 0x00})));
-
-        // half-precision float
-        //CHECK(json::to_cbor(json::parse("-4.0")) == std::vector<uint8_t>({0xf9, 0xc4, 0x00}));
+        CHECK(json::parse("5.960464477539063e-8") == json::from_cbor(std::vector<uint8_t>({0xf9, 0x00, 0x01})));
+        CHECK(json::parse("0.00006103515625") == json::from_cbor(std::vector<uint8_t>({0xf9, 0x04, 0x00})));
         CHECK(json::parse("-4.0") == json::from_cbor(std::vector<uint8_t>({0xf9, 0xc4, 0x00})));
 
         CHECK(json::to_cbor(json::parse("-4.1")) == std::vector<uint8_t>({0xfb, 0xc0, 0x10, 0x66, 0x66, 0x66, 0x66, 0x66, 0x66}));

tests/src/unit-conversions.cpp

@@ -1380,21 +1380,22 @@ TEST_CASE("value conversion")
 
             SECTION("std::map")
             {
-                j1.get<std::map<std::string, int>>();
-                j2.get<std::map<std::string, unsigned int>>();
-                j3.get<std::map<std::string, double>>();
-                j4.get<std::map<std::string, bool>>();
-                j5.get<std::map<std::string, std::string>>();
+                CHECK(j1.get<std::map<std::string, int>>() == (std::map<std::string, int> {{"one", 1}, {"two", 2}, {"three", 3}}));
+                CHECK(j2.get<std::map<std::string, unsigned int>>() == (std::map<std::string, unsigned int> {{"one", 1u}, {"two", 2u}, {"three", 3u}}));
+                CHECK(j3.get<std::map<std::string, double>>() == (std::map<std::string, double> {{"one", 1.1}, {"two", 2.2}, {"three", 3.3}}));
+                CHECK(j4.get<std::map<std::string, bool>>() == (std::map<std::string, bool> {{"one", true}, {"two", false}, {"three", true}}));
+                CHECK(j5.get<std::map<std::string, std::string>>() == (std::map<std::string, std::string> {{"one", "eins"}, {"two", "zwei"}, {"three", "drei"}}));
             }
 
             SECTION("std::unordered_map")
             {
-                j1.get<std::unordered_map<std::string, int>>();
-                j2.get<std::unordered_map<std::string, unsigned int>>();
-                j3.get<std::unordered_map<std::string, double>>();
-                j4.get<std::unordered_map<std::string, bool>>();
-                j5.get<std::unordered_map<std::string, std::string>>();
-                // CHECK(m5["one"] == "eins");
+                CHECK(j1.get<std::unordered_map<std::string, int>>() == (std::unordered_map<std::string, int> {{"one", 1}, {"two", 2}, {"three", 3}}));
+                CHECK(j2.get<std::unordered_map<std::string, unsigned int>>() == (std::unordered_map<std::string, unsigned int> {{"one", 1u}, {"two", 2u}, {"three", 3u}}));
+                CHECK(j3.get<std::unordered_map<std::string, double>>() == (std::unordered_map<std::string, double> {{"one", 1.1}, {"two", 2.2}, {"three", 3.3}}));
+                CHECK(j4.get<std::unordered_map<std::string, bool>>() == (std::unordered_map<std::string, bool> {{"one", true}, {"two", false}, {"three", true}}));
+                const auto m5 = j5.get<std::unordered_map<std::string, std::string>>();
+                CHECK(m5 == (std::unordered_map<std::string, std::string> {{"one", "eins"}, {"two", "zwei"}, {"three", "drei"}}));
+                CHECK(m5.at("one") == "eins");
             }
 
             SECTION("reserve is called on containers that support it (#5406)")
@@ -1430,22 +1431,24 @@ TEST_CASE("value conversion")
 
             SECTION("std::multimap")
             {
-                j1.get<std::multimap<std::string, int>>();
-                j2.get<std::multimap<std::string, unsigned int>>();
-                j3.get<std::multimap<std::string, double>>();
-                j4.get<std::multimap<std::string, bool>>();
-                j5.get<std::multimap<std::string, std::string>>();
-                // CHECK(m5["one"] == "eins");
+                CHECK(j1.get<std::multimap<std::string, int>>() == (std::multimap<std::string, int> {{"one", 1}, {"two", 2}, {"three", 3}}));
+                CHECK(j2.get<std::multimap<std::string, unsigned int>>() == (std::multimap<std::string, unsigned int> {{"one", 1u}, {"two", 2u}, {"three", 3u}}));
+                CHECK(j3.get<std::multimap<std::string, double>>() == (std::multimap<std::string, double> {{"one", 1.1}, {"two", 2.2}, {"three", 3.3}}));
+                CHECK(j4.get<std::multimap<std::string, bool>>() == (std::multimap<std::string, bool> {{"one", true}, {"two", false}, {"three", true}}));
+                const auto m5 = j5.get<std::multimap<std::string, std::string>>();
+                CHECK(m5 == (std::multimap<std::string, std::string> {{"one", "eins"}, {"two", "zwei"}, {"three", "drei"}}));
+                CHECK(m5.find("one")->second == "eins");
             }
 
             SECTION("std::unordered_multimap")
             {
-                j1.get<std::unordered_multimap<std::string, int>>();
-                j2.get<std::unordered_multimap<std::string, unsigned int>>();
-                j3.get<std::unordered_multimap<std::string, double>>();
-                j4.get<std::unordered_multimap<std::string, bool>>();
-                j5.get<std::unordered_multimap<std::string, std::string>>();
-                // CHECK(m5["one"] == "eins");
+                CHECK(j1.get<std::unordered_multimap<std::string, int>>() == (std::unordered_multimap<std::string, int> {{"one", 1}, {"two", 2}, {"three", 3}}));
+                CHECK(j2.get<std::unordered_multimap<std::string, unsigned int>>() == (std::unordered_multimap<std::string, unsigned int> {{"one", 1u}, {"two", 2u}, {"three", 3u}}));
+                CHECK(j3.get<std::unordered_multimap<std::string, double>>() == (std::unordered_multimap<std::string, double> {{"one", 1.1}, {"two", 2.2}, {"three", 3.3}}));
+                CHECK(j4.get<std::unordered_multimap<std::string, bool>>() == (std::unordered_multimap<std::string, bool> {{"one", true}, {"two", false}, {"three", true}}));
+                const auto m5 = j5.get<std::unordered_multimap<std::string, std::string>>();
+                CHECK(m5 == (std::unordered_multimap<std::string, std::string> {{"one", "eins"}, {"two", "zwei"}, {"three", "drei"}}));
+                CHECK(m5.find("one")->second == "eins");
             }
 
             SECTION("exception in case of a non-object type")
@@ -1466,29 +1469,30 @@ TEST_CASE("value conversion")
 
             SECTION("std::list")
             {
-                j1.get<std::list<int>>();
-                j2.get<std::list<unsigned int>>();
-                j3.get<std::list<double>>();
-                j4.get<std::list<bool>>();
-                j5.get<std::list<std::string>>();
+                CHECK(j1.get<std::list<int>>() == (std::list<int> {1, 2, 3, 4}));
+                CHECK(j2.get<std::list<unsigned int>>() == (std::list<unsigned int> {1u, 2u, 3u, 4u}));
+                CHECK(j3.get<std::list<double>>() == (std::list<double> {1.2, 2.3, 3.4, 4.5}));
+                CHECK(j4.get<std::list<bool>>() == (std::list<bool> {true, false, true}));
+                CHECK(j5.get<std::list<std::string>>() == (std::list<std::string> {"one", "two", "three"}));
             }
 
             SECTION("std::forward_list")
             {
-                j1.get<std::forward_list<int>>();
-                j2.get<std::forward_list<unsigned int>>();
-                j3.get<std::forward_list<double>>();
-                j4.get<std::forward_list<bool>>();
-                j5.get<std::forward_list<std::string>>();
+                CHECK(j1.get<std::forward_list<int>>() == (std::forward_list<int> {1, 2, 3, 4}));
+                CHECK(j2.get<std::forward_list<unsigned int>>() == (std::forward_list<unsigned int> {1u, 2u, 3u, 4u}));
+                CHECK(j3.get<std::forward_list<double>>() == (std::forward_list<double> {1.2, 2.3, 3.4, 4.5}));
+                CHECK(j4.get<std::forward_list<bool>>() == (std::forward_list<bool> {true, false, true}));
+                CHECK(j5.get<std::forward_list<std::string>>() == (std::forward_list<std::string> {"one", "two", "three"}));
             }
 
             SECTION("std::array")
             {
-                j1.get<std::array<int, 4>>();
-                j2.get<std::array<unsigned int, 3>>();
-                j3.get<std::array<double, 4>>();
-                j4.get<std::array<bool, 3>>();
-                j5.get<std::array<std::string, 3>>();
+                CHECK(j1.get<std::array<int, 4>>() == (std::array<int, 4> {{1, 2, 3, 4}}));
+                // only the first 3 elements of j2 are converted, since the target array is smaller
+                CHECK(j2.get<std::array<unsigned int, 3>>() == (std::array<unsigned int, 3> {{1u, 2u, 3u}}));
+                CHECK(j3.get<std::array<double, 4>>() == (std::array<double, 4> {{1.2, 2.3, 3.4, 4.5}}));
+                CHECK(j4.get<std::array<bool, 3>>() == (std::array<bool, 3> {{true, false, true}}));
+                CHECK(j5.get<std::array<std::string, 3>>() == (std::array<std::string, 3> {{"one", "two", "three"}}));
 
                 SECTION("std::array is larger than JSON")
                 {
@@ -1508,47 +1512,53 @@ TEST_CASE("value conversion")
 
             SECTION("std::valarray")
             {
-                j1.get<std::valarray<int>>();
-                j2.get<std::valarray<unsigned int>>();
-                j3.get<std::valarray<double>>();
-                j4.get<std::valarray<bool>>();
-                j5.get<std::valarray<std::string>>();
+                // valarray has no operator== that returns bool, so compare via a vector copy
+                const auto v1 = j1.get<std::valarray<int>>();
+                CHECK((std::vector<int>(std::begin(v1), std::end(v1)) == std::vector<int> {1, 2, 3, 4}));
+                const auto v2 = j2.get<std::valarray<unsigned int>>();
+                CHECK((std::vector<unsigned int>(std::begin(v2), std::end(v2)) == std::vector<unsigned int> {1u, 2u, 3u, 4u}));
+                const auto v3 = j3.get<std::valarray<double>>();
+                CHECK((std::vector<double>(std::begin(v3), std::end(v3)) == std::vector<double> {1.2, 2.3, 3.4, 4.5}));
+                const auto v4 = j4.get<std::valarray<bool>>();
+                CHECK((std::vector<bool>(std::begin(v4), std::end(v4)) == std::vector<bool> {true, false, true}));
+                const auto v5 = j5.get<std::valarray<std::string>>();
+                CHECK((std::vector<std::string>(std::begin(v5), std::end(v5)) == std::vector<std::string> {"one", "two", "three"}));
             }
 
             SECTION("std::vector")
             {
-                j1.get<std::vector<int>>();
-                j2.get<std::vector<unsigned int>>();
-                j3.get<std::vector<double>>();
-                j4.get<std::vector<bool>>();
-                j5.get<std::vector<std::string>>();
+                CHECK(j1.get<std::vector<int>>() == (std::vector<int> {1, 2, 3, 4}));
+                CHECK(j2.get<std::vector<unsigned int>>() == (std::vector<unsigned int> {1u, 2u, 3u, 4u}));
+                CHECK(j3.get<std::vector<double>>() == (std::vector<double> {1.2, 2.3, 3.4, 4.5}));
+                CHECK(j4.get<std::vector<bool>>() == (std::vector<bool> {true, false, true}));
+                CHECK(j5.get<std::vector<std::string>>() == (std::vector<std::string> {"one", "two", "three"}));
             }
 
             SECTION("std::deque")
             {
-                j1.get<std::deque<int>>();
-                j2.get<std::deque<unsigned int>>();
-                j2.get<std::deque<double>>();
-                j4.get<std::deque<bool>>();
-                j5.get<std::deque<std::string>>();
+                CHECK(j1.get<std::deque<int>>() == (std::deque<int> {1, 2, 3, 4}));
+                CHECK(j2.get<std::deque<unsigned int>>() == (std::deque<unsigned int> {1u, 2u, 3u, 4u}));
+                CHECK(j3.get<std::deque<double>>() == (std::deque<double> {1.2, 2.3, 3.4, 4.5}));
+                CHECK(j4.get<std::deque<bool>>() == (std::deque<bool> {true, false, true}));
+                CHECK(j5.get<std::deque<std::string>>() == (std::deque<std::string> {"one", "two", "three"}));
             }
 
             SECTION("std::set")
             {
-                j1.get<std::set<int>>();
-                j2.get<std::set<unsigned int>>();
-                j3.get<std::set<double>>();
-                j4.get<std::set<bool>>();
-                j5.get<std::set<std::string>>();
+                CHECK(j1.get<std::set<int>>() == (std::set<int> {1, 2, 3, 4}));
+                CHECK(j2.get<std::set<unsigned int>>() == (std::set<unsigned int> {1u, 2u, 3u, 4u}));
+                CHECK(j3.get<std::set<double>>() == (std::set<double> {1.2, 2.3, 3.4, 4.5}));
+                CHECK(j4.get<std::set<bool>>() == (std::set<bool> {true, false, true}));
+                CHECK(j5.get<std::set<std::string>>() == (std::set<std::string> {"one", "two", "three"}));
             }
 
             SECTION("std::unordered_set")
             {
-                j1.get<std::unordered_set<int>>();
-                j2.get<std::unordered_set<unsigned int>>();
-                j3.get<std::unordered_set<double>>();
-                j4.get<std::unordered_set<bool>>();
-                j5.get<std::unordered_set<std::string>>();
+                CHECK(j1.get<std::unordered_set<int>>() == (std::unordered_set<int> {1, 2, 3, 4}));
+                CHECK(j2.get<std::unordered_set<unsigned int>>() == (std::unordered_set<unsigned int> {1u, 2u, 3u, 4u}));
+                CHECK(j3.get<std::unordered_set<double>>() == (std::unordered_set<double> {1.2, 2.3, 3.4, 4.5}));
+                CHECK(j4.get<std::unordered_set<bool>>() == (std::unordered_set<bool> {true, false, true}));
+                CHECK(j5.get<std::unordered_set<std::string>>() == (std::unordered_set<std::string> {"one", "two", "three"}));
             }
 
             SECTION("std::map (array of pairs)")

tests/src/unit-deserialization.cpp

@@ -28,11 +28,6 @@ using nlohmann::json;
 #include <string>
 #include <valarray>
 
-#if defined(_WIN32)
-    #define NOMINMAX
-    #include <windows.h> // for GetACP()
-#endif
-
 namespace
 {
 struct SaxEventLogger : public nlohmann::json_sax<json>
@@ -228,24 +223,6 @@ class proxy_iterator
     iterator* m_it = nullptr;
 };
 
-// JSON_HAS_CPP_20
-#if defined(__cpp_char8_t)
-bool check_utf8()
-{
-#if defined(_WIN32)
-    // Runtime check of the active ANSI code page
-    // 65001 == UTF-8
-    return GetACP() == 65001;
-#elif defined(__ICC) || defined(__INTEL_COMPILER)
-    // classic Intel ICC does not encode narrow string literals containing
-    // non-ASCII source characters as UTF-8, so comparing a decoded u8 literal
-    // against a narrow string literal containing the same characters fails
-    return false;
-#else
-    return true;
-#endif
-}
-#endif
 } // namespace
 
 TEST_CASE("deserialization")
@@ -1328,14 +1305,15 @@ TEST_CASE("deserialization")
         CHECK(j1["key"] == "value");
         CHECK(j1["num"] == 42);
 
-        // UTF-8 prefixed literal (C++20 and later);
-        // MSVC may not set /utf-8, so we need to check
-        if (check_utf8())
-        {
-            const auto j2 = u8R"({"emoji": "😀", "msg": "hello"})"_json;
-            CHECK(j2["emoji"] == "😀");
-            CHECK(j2["msg"] == "hello");
-        }
+        // UTF-8 prefixed literal (C++20 and later); the emoji is written as a
+        // \U escape rather than a raw multibyte character so this does not
+        // depend on the compiler's source-file encoding (e.g., MSVC without
+        // /utf-8, or classic ICC, which does not encode non-ASCII narrow
+        // string literals as UTF-8 - compare against a \x-escaped expectation
+        // for the same reason)
+        const auto j2 = u8"{\"emoji\": \"\U0001F600\", \"msg\": \"hello\"}"_json;
+        CHECK(j2["emoji"] == "\xF0\x9F\x98\x80");
+        CHECK(j2["msg"] == "hello");
 
         const auto j3 = u8R"({"key": "value", "num": 42})"_json;
         CHECK(j3["key"] == "value");

tests/src/unit-iterators2.cpp

@@ -893,8 +893,6 @@ TEST_CASE("iterators 2")
             CHECK(std::ranges::input_range<items_type>);
         }
 
-        // libstdc++ algorithms don't work with Clang 15 (04/2022)
-#if !DOCTEST_CLANG || (DOCTEST_CLANG && defined(__GLIBCXX__))
         SECTION("algorithms")
         {
             SECTION("copy")
@@ -929,11 +927,7 @@ TEST_CASE("iterators 2")
                 CHECK(*it == 2);
             }
         }
-#endif
 
-        // libstdc++ views don't work with Clang 15 (04/2022)
-        // libc++ hides limited ranges implementation behind guard macro
-#if !(DOCTEST_CLANG && (defined(__GLIBCXX__) || defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)))
         SECTION("views")
         {
             SECTION("reverse")
@@ -966,7 +960,6 @@ TEST_CASE("iterators 2")
                 CHECK(j_transformed == j_expected);
             }
         }
-#endif
     }
 #endif
 }

tests/src/unit-msgpack.cpp

@@ -21,85 +21,11 @@ using nlohmann::json;
 #include <limits>
 #include <set>
 #include "make_test_data_available.hpp"
+#include "round_trip_corpus.hpp"
 #include "test_utils.hpp"
+#include "sax_countdown.hpp"
+using utils::SaxCountdown;
 
-namespace
-{
-class SaxCountdown
-{
-  public:
-    explicit SaxCountdown(const int count) : events_left(count)
-    {}
-
-    bool null()
-    {
-        return events_left-- > 0;
-    }
-
-    bool boolean(bool /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_integer(json::number_integer_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_unsigned(json::number_unsigned_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_float(json::number_float_t /*unused*/, const std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool string(std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool binary(std::vector<std::uint8_t>& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool start_object(std::size_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool key(std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool end_object()
-    {
-        return events_left-- > 0;
-    }
-
-    bool start_array(std::size_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool end_array()
-    {
-        return events_left-- > 0;
-    }
-
-    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/, const json::exception& /*unused*/) // NOLINT(readability-convert-member-functions-to-static)
-    {
-        return false;
-    }
-
-  private:
-    int events_left = 0;
-};
-} // namespace
 
 TEST_CASE("MessagePack")
 {
@@ -1930,6 +1856,38 @@ TEST_CASE("Parse MessagePack directly from a file using iterator and sentinel")
     CHECK((parsed.is_object() || parsed.is_array()));
 }
 
+TEST_CASE("MessagePack round-trip invariants")
+{
+    // This checks what the parse_msgpack_fuzzer driver checks (see
+    // tests/src/fuzzer-parse_msgpack.cpp), so that a regression shows up in
+    // CI rather than as an OSS-Fuzz report: anything from_msgpack() returns
+    // (j1) can be serialized, parsed back (j2), and serialized again to
+    // reproduce the exact bytes.
+    for (const auto& j0 : utils::round_trip_corpus::values())
+    {
+        json j1;
+        try
+        {
+            // turn the corpus value into a value as from_msgpack() returns it
+            j1 = json::from_msgpack(json::to_msgpack(j0));
+        }
+        catch (const json::exception&)
+        {
+            // the fuzzer driver only ever sees values from_msgpack() actually
+            // produced, so skip corpus values that do not survive the
+            // round trip here, too
+            continue;
+        }
+
+        INFO("j1 = " << j1.dump());
+        const std::vector<std::uint8_t> vec = json::to_msgpack(j1);
+        json j2;
+        // anything the library writes must be parsable by the library
+        REQUIRE_NOTHROW(j2 = json::from_msgpack(vec));
+        CHECK(json::to_msgpack(j2) == vec);
+    }
+}
+
 TEST_CASE("MessagePack roundtrips" * doctest::skip())
 {
     SECTION("input from msgpack-python")

tests/src/unit-readme.cpp

@@ -28,7 +28,7 @@ using nlohmann::json;
 DOCTEST_MSVC_SUPPRESS_WARNING_PUSH
 DOCTEST_MSVC_SUPPRESS_WARNING(4189)
 
-TEST_CASE("README" * doctest::skip())
+TEST_CASE("README")
 {
     {
         // redirect std::cout for the README file

tests/src/unit-regression1.cpp

@@ -1482,7 +1482,23 @@ TEST_CASE("regression tests 1")
 
     SECTION("issue #972 - Segmentation fault on G++ when trying to assign json string literal to custom json type")
     {
+        // this assignment used to crash outright
         my_json const foo = R"([1, 2, 3])"_json;
+
+        // fifo_map is the adapter the docs recommend for keeping object keys
+        // in insertion order (see docs/mkdocs/docs/features/object_order.md
+        // and docs/mkdocs/docs/features/types/template_parameters.md); check
+        // that recommendation actually holds, including through erase() and
+        // inserting a new key. The comparator is stateful, so this avoids
+        // deep copies of "order" (see #1763, #5649).
+        my_json order = my_json::parse(R"({"z":1,"a":2,"m":{"y":1,"b":2}})");
+        CHECK(order.dump() == R"({"z":1,"a":2,"m":{"y":1,"b":2}})");
+
+        order.erase("z");
+        CHECK(order.dump() == R"({"a":2,"m":{"y":1,"b":2}})");
+
+        order["new_key"] = 3;
+        CHECK(order.dump() == R"({"a":2,"m":{"y":1,"b":2},"new_key":3})");
     }
 
     SECTION("issue #977 - Assigning between different json types")

tests/src/unit-regression2.cpp

@@ -213,28 +213,6 @@ struct adl_serializer<NonDefaultConstructible>
 };
 }  // namespace nlohmann
 
-/////////////////////////////////////////////////////////////////////
-// for #2824
-/////////////////////////////////////////////////////////////////////
-
-class sax_no_exception : public nlohmann::detail::json_sax_dom_parser<json, nlohmann::detail::string_input_adapter_type>
-{
-  public:
-    explicit sax_no_exception(json& j)
-        : nlohmann::detail::json_sax_dom_parser<json, nlohmann::detail::string_input_adapter_type>(j, false)
-    {}
-
-    static bool parse_error(std::size_t /*position*/, const std::string& /*last_token*/, const json::exception& ex)
-    {
-        error_string = new std::string(ex.what());  // NOLINT(cppcoreguidelines-owning-memory)
-        return false;
-    }
-
-    static std::string* error_string;
-};
-
-std::string* sax_no_exception::error_string = nullptr;
-
 /////////////////////////////////////////////////////////////////////
 // for #2982
 /////////////////////////////////////////////////////////////////////
@@ -751,16 +729,6 @@ TEST_CASE("regression tests 2")
         }
     }
 
-    SECTION("issue #2824 - encoding of json::exception::what()")
-    {
-        json j;
-        sax_no_exception sax(j);
-
-        CHECK(!json::sax_parse("xyz", &sax));
-        CHECK(*sax_no_exception::error_string == "[json.exception.parse_error.101] parse error at line 1, column 1: syntax error while parsing value - invalid literal; last read: 'x'");
-        delete sax_no_exception::error_string;  // NOLINT(cppcoreguidelines-owning-memory)
-    }
-
     SECTION("issue #2825 - Properly constrain the basic_json conversion operator")
     {
         static_assert(std::is_copy_assignable<nlohmann::ordered_json>::value, "ordered_json must be copy assignable");

tests/src/unit-ubjson.cpp

@@ -17,84 +17,9 @@ using nlohmann::json;
 #include "make_test_data_available.hpp"
 #include "round_trip_corpus.hpp"
 #include "test_utils.hpp"
+#include "sax_countdown.hpp"
+using utils::SaxCountdown;
 
-namespace
-{
-class SaxCountdown
-{
-  public:
-    explicit SaxCountdown(const int count) : events_left(count)
-    {}
-
-    bool null()
-    {
-        return events_left-- > 0;
-    }
-
-    bool boolean(bool /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_integer(json::number_integer_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_unsigned(json::number_unsigned_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool number_float(json::number_float_t /*unused*/, const std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool string(std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool binary(std::vector<std::uint8_t>& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool start_object(std::size_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool key(std::string& /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool end_object()
-    {
-        return events_left-- > 0;
-    }
-
-    bool start_array(std::size_t /*unused*/)
-    {
-        return events_left-- > 0;
-    }
-
-    bool end_array()
-    {
-        return events_left-- > 0;
-    }
-
-    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/, const json::exception& /*unused*/) // NOLINT(readability-convert-member-functions-to-static)
-    {
-        return false;
-    }
-
-  private:
-    int events_left = 0;
-};
-} // namespace
 
 TEST_CASE("UBJSON")
 {

tests/src/unit-wstring.cpp

@@ -11,135 +11,97 @@
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 
-// ICPC errors out on multibyte character sequences in source files
-#ifndef __INTEL_COMPILER
-namespace
-{
-bool wstring_is_utf16();
-bool wstring_is_utf16()
-{
-    return (std::wstring(L"💩") == std::wstring(L"\U0001F4A9"));
-}
-
-bool u16string_is_utf16();
-bool u16string_is_utf16()
-{
-    return (std::u16string(u"💩") == std::u16string(u"\U0001F4A9"));
-}
-
-bool u32string_is_utf32();
-bool u32string_is_utf32()
-{
-    return (std::u32string(U"💩") == std::u32string(U"\U0001F4A9"));
-}
-} // namespace
-
 TEST_CASE("wide strings")
 {
     SECTION("std::wstring")
     {
-        if (wstring_is_utf16())
-        {
-            std::wstring const w = L"[12.2,\"Ⴥaäö💤🧢\"]";
-            json const j = json::parse(w);
-            CHECK(j.dump() == "[12.2,\"Ⴥaäö💤🧢\"]");
-        }
+        // U+10C5 U+0061(a) U+00E4 U+00F6 U+1F4A4 U+1F9E2, written with \u/\U
+        // escapes rather than as raw multibyte characters so this file
+        // compiles on toolchains (e.g. classic ICC) that error out on
+        // multibyte character sequences in source files
+        std::wstring const w = L"[12.2,\"\u10C5a\u00E4\u00F6\U0001F4A4\U0001F9E2\"]";
+        json const j = json::parse(w);
+        CHECK(j.dump() == "[12.2,\"" "\xE1\x83\x85" "a" "\xC3\xA4" "\xC3\xB6" "\xF0\x9F\x92\xA4" "\xF0\x9F\xA7\xA2" "\"]");
     }
 
     SECTION("invalid std::wstring")
     {
-        if (wstring_is_utf16())
-        {
-            std::wstring const w = L"\"\xDBFF";
-            json _;
-            CHECK_THROWS_AS(_ = json::parse(w), json::parse_error&);
+        std::wstring const w = L"\"\xDBFF";
+        json _;
+        CHECK_THROWS_AS(_ = json::parse(w), json::parse_error&);
 
-            // the exact message depends on the width of wchar_t: a 16-bit
-            // wchar_t passes the lone surrogate to the UTF-8 decoder unchanged
-            // (rejected as a single ill-formed byte at column 2), while a
-            // 32-bit wchar_t first encodes it as an ill-formed three-byte
-            // sequence (rejected one byte later, at column 3)
-            const char* const error_low_surrogate = sizeof(wchar_t) == 2
-                                                    ? "[json.exception.parse_error.101] parse error at line 1, column 2: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"<U+0000>'"
-                                                    : "[json.exception.parse_error.101] parse error at line 1, column 3: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"\xED\xB0'";
-            const char* const error_high_surrogate = sizeof(wchar_t) == 2
-                ? "[json.exception.parse_error.101] parse error at line 1, column 2: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"<U+0000>'"
-                : "[json.exception.parse_error.101] parse error at line 1, column 3: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"\xED\xA0'";
+        // the exact message depends on the width of wchar_t: a 16-bit
+        // wchar_t passes the lone surrogate to the UTF-8 decoder unchanged
+        // (rejected as a single ill-formed byte at column 2), while a
+        // 32-bit wchar_t first encodes it as an ill-formed three-byte
+        // sequence (rejected one byte later, at column 3)
+        const char* const error_low_surrogate = sizeof(wchar_t) == 2
+                                                ? "[json.exception.parse_error.101] parse error at line 1, column 2: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"<U+0000>'"
+                                                : "[json.exception.parse_error.101] parse error at line 1, column 3: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"\xED\xB0'";
+        const char* const error_high_surrogate = sizeof(wchar_t) == 2
+            ? "[json.exception.parse_error.101] parse error at line 1, column 2: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"<U+0000>'"
+            : "[json.exception.parse_error.101] parse error at line 1, column 3: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"\xED\xA0'";
 
-            // a lone low surrogate cannot start a pair
-            CHECK_THROWS_WITH_AS(_ = json::parse(std::wstring{L'"', static_cast<wchar_t>(0xDC00), L'"'}), error_low_surrogate, json::parse_error&);
-            // a high surrogate followed by a non-low-surrogate unit is invalid
-            CHECK_THROWS_WITH_AS(_ = json::parse(std::wstring{L'"', static_cast<wchar_t>(0xD800), L'a', L'"'}), error_high_surrogate, json::parse_error&);
-            // ... also when the unit is above the low surrogates
-            CHECK_THROWS_WITH_AS(_ = json::parse(std::wstring{L'"', static_cast<wchar_t>(0xD800), static_cast<wchar_t>(0xE000), L'"'}), error_high_surrogate, json::parse_error&);
-            // a lone low surrogate must not swallow the following unit: pairing
-            // it with any second unit would produce valid UTF-8, so the error
-            // has to report an ill-formed byte at the surrogate's own position
-            CHECK_THROWS_WITH_AS(_ = json::parse(std::wstring{L'"', static_cast<wchar_t>(0xDC00), L'a', L'"'}), error_low_surrogate, json::parse_error&);
-        }
+        // a lone low surrogate cannot start a pair
+        CHECK_THROWS_WITH_AS(_ = json::parse(std::wstring{L'"', static_cast<wchar_t>(0xDC00), L'"'}), error_low_surrogate, json::parse_error&);
+        // a high surrogate followed by a non-low-surrogate unit is invalid
+        CHECK_THROWS_WITH_AS(_ = json::parse(std::wstring{L'"', static_cast<wchar_t>(0xD800), L'a', L'"'}), error_high_surrogate, json::parse_error&);
+        // ... also when the unit is above the low surrogates
+        CHECK_THROWS_WITH_AS(_ = json::parse(std::wstring{L'"', static_cast<wchar_t>(0xD800), static_cast<wchar_t>(0xE000), L'"'}), error_high_surrogate, json::parse_error&);
+        // a lone low surrogate must not swallow the following unit: pairing
+        // it with any second unit would produce valid UTF-8, so the error
+        // has to report an ill-formed byte at the surrogate's own position
+        CHECK_THROWS_WITH_AS(_ = json::parse(std::wstring{L'"', static_cast<wchar_t>(0xDC00), L'a', L'"'}), error_low_surrogate, json::parse_error&);
     }
 
     SECTION("std::u16string")
     {
-        if (u16string_is_utf16())
-        {
-            std::u16string const w = u"[12.2,\"Ⴥaäö💤🧢\"]";
-            json const j = json::parse(w);
-            CHECK(j.dump() == "[12.2,\"Ⴥaäö💤🧢\"]");
-        }
+        std::u16string const w = u"[12.2,\"\u10C5a\u00E4\u00F6\U0001F4A4\U0001F9E2\"]";
+        json const j = json::parse(w);
+        CHECK(j.dump() == "[12.2,\"" "\xE1\x83\x85" "a" "\xC3\xA4" "\xC3\xB6" "\xF0\x9F\x92\xA4" "\xF0\x9F\xA7\xA2" "\"]");
     }
 
     SECTION("invalid std::u16string")
     {
-        if (u16string_is_utf16())
-        {
-            std::u16string const w = u"\"\xDBFF";
-            json _;
-            CHECK_THROWS_AS(_ = json::parse(w), json::parse_error&);
+        std::u16string const w = u"\"\xDBFF";
+        json _;
+        CHECK_THROWS_AS(_ = json::parse(w), json::parse_error&);
 
-            // a lone low surrogate cannot start a pair
-            CHECK_THROWS_WITH_AS(_ = json::parse(std::u16string{u'"', 0xDC00, u'"'}), "[json.exception.parse_error.101] parse error at line 1, column 2: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"<U+0000>'", json::parse_error&);
-            // a high surrogate followed by a non-low-surrogate unit is invalid
-            CHECK_THROWS_WITH_AS(_ = json::parse(std::u16string{u'"', 0xD800, u'a', u'"'}), "[json.exception.parse_error.101] parse error at line 1, column 2: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"<U+0000>'", json::parse_error&);
-            // ... also when the unit is above the low surrogates
-            CHECK_THROWS_WITH_AS(_ = json::parse(std::u16string{u'"', 0xD800, 0xE000, u'"'}), "[json.exception.parse_error.101] parse error at line 1, column 2: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"<U+0000>'", json::parse_error&);
-            // a lone low surrogate must not swallow the following unit: pairing
-            // it with any second unit would produce valid UTF-8, so the error
-            // has to report an ill-formed byte at the surrogate's own position
-            CHECK_THROWS_WITH_AS(_ = json::parse(std::u16string{u'"', 0xDC00, u'a', u'"'}), "[json.exception.parse_error.101] parse error at line 1, column 2: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"<U+0000>'", json::parse_error&);
-            // a valid surrogate pair is still decoded (U+1F600)
-            CHECK(json::parse(std::u16string{u'"', 0xD83D, 0xDE00, u'"'}).get<std::string>() == "\xF0\x9F\x98\x80");
-        }
+        // a lone low surrogate cannot start a pair
+        CHECK_THROWS_WITH_AS(_ = json::parse(std::u16string{u'"', 0xDC00, u'"'}), "[json.exception.parse_error.101] parse error at line 1, column 2: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"<U+0000>'", json::parse_error&);
+        // a high surrogate followed by a non-low-surrogate unit is invalid
+        CHECK_THROWS_WITH_AS(_ = json::parse(std::u16string{u'"', 0xD800, u'a', u'"'}), "[json.exception.parse_error.101] parse error at line 1, column 2: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"<U+0000>'", json::parse_error&);
+        // ... also when the unit is above the low surrogates
+        CHECK_THROWS_WITH_AS(_ = json::parse(std::u16string{u'"', 0xD800, 0xE000, u'"'}), "[json.exception.parse_error.101] parse error at line 1, column 2: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"<U+0000>'", json::parse_error&);
+        // a lone low surrogate must not swallow the following unit: pairing
+        // it with any second unit would produce valid UTF-8, so the error
+        // has to report an ill-formed byte at the surrogate's own position
+        CHECK_THROWS_WITH_AS(_ = json::parse(std::u16string{u'"', 0xDC00, u'a', u'"'}), "[json.exception.parse_error.101] parse error at line 1, column 2: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"<U+0000>'", json::parse_error&);
+        // a valid surrogate pair is still decoded (U+1F600)
+        CHECK(json::parse(std::u16string{u'"', 0xD83D, 0xDE00, u'"'}).get<std::string>() == "\xF0\x9F\x98\x80");
     }
 
     SECTION("std::u32string")
     {
-        if (u32string_is_utf32())
-        {
-            std::u32string const w = U"[12.2,\"Ⴥaäö💤🧢\"]";
-            json const j = json::parse(w);
-            CHECK(j.dump() == "[12.2,\"Ⴥaäö💤🧢\"]");
-        }
+        std::u32string const w = U"[12.2,\"\u10C5a\u00E4\u00F6\U0001F4A4\U0001F9E2\"]";
+        json const j = json::parse(w);
+        CHECK(j.dump() == "[12.2,\"" "\xE1\x83\x85" "a" "\xC3\xA4" "\xC3\xB6" "\xF0\x9F\x92\xA4" "\xF0\x9F\xA7\xA2" "\"]");
     }
 
     SECTION("invalid std::u32string")
     {
-        if (u32string_is_utf32())
-        {
-            std::u32string const w = U"\"\x110000";
-            json _;
-            CHECK_THROWS_AS(_ = json::parse(w), json::parse_error&);
+        std::u32string const w = U"\"\x110000";
+        json _;
+        CHECK_THROWS_AS(_ = json::parse(w), json::parse_error&);
 
-            // a code unit above U+10FFFF must not be narrowed onto the EOF
-            // sentinel: 0xFFFFFFFF would otherwise end the document silently and
-            // let everything following it pass the strict end-of-input check
-            std::u32string const trailing{U'[', U'1', U']', static_cast<char32_t>(0xFFFFFFFF), U'x'};
-            CHECK_THROWS_WITH_AS(_ = json::parse(trailing), "[json.exception.parse_error.101] parse error at line 1, column 4: syntax error while parsing value - invalid literal; last read: '1]\xFF'; expected end of input", json::parse_error&);
-            CHECK(!json::accept(trailing));
+        // a code unit above U+10FFFF must not be narrowed onto the EOF
+        // sentinel: 0xFFFFFFFF would otherwise end the document silently and
+        // let everything following it pass the strict end-of-input check
+        std::u32string const trailing{U'[', U'1', U']', static_cast<char32_t>(0xFFFFFFFF), U'x'};
+        CHECK_THROWS_WITH_AS(_ = json::parse(trailing), "[json.exception.parse_error.101] parse error at line 1, column 4: syntax error while parsing value - invalid literal; last read: '1]\xFF'; expected end of input", json::parse_error&);
+        CHECK(!json::accept(trailing));
 
-            // the same unit inside a string is reported as an ill-formed byte
-            CHECK_THROWS_WITH_AS(_ = json::parse(std::u32string{U'"', static_cast<char32_t>(0xFFFFFFFF), U'"'}), "[json.exception.parse_error.101] parse error at line 1, column 2: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"\xFF'", json::parse_error&);
-        }
+        // the same unit inside a string is reported as an ill-formed byte
+        CHECK_THROWS_WITH_AS(_ = json::parse(std::u32string{U'"', static_cast<char32_t>(0xFFFFFFFF), U'"'}), "[json.exception.parse_error.101] parse error at line 1, column 2: syntax error while parsing value - invalid string: ill-formed UTF-8 byte; last read: '\"\xFF'", json::parse_error&);
     }
 }
-#endif

tests/src/value_in_range_of_test.hpp

@@ -0,0 +1,92 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++ (supporting code)
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+// shared between unit-32bit.cpp (which must keep including this header,
+// because JSON_32bitTest=ONLY builds only that file) and unit-bjdata.cpp
+
+#include <climits> // CHAR_BIT
+#include <limits>
+#include <string>
+#include <type_traits>
+
+#include <nlohmann/json.hpp>
+
+template <typename OfType, typename T, bool MinInRange, bool MaxInRange>
+struct trait_test_arg
+{
+    using of_type = OfType;
+    using type = T;
+    static constexpr bool min_in_range = MinInRange;
+    static constexpr bool max_in_range = MaxInRange;
+};
+
+TEST_CASE_TEMPLATE_DEFINE("value_in_range_of trait", T, value_in_range_of_test) // NOLINT(readability-math-missing-parentheses)
+{
+    using nlohmann::detail::value_in_range_of;
+
+    using of_type = typename T::of_type;
+    using type = typename T::type;
+    constexpr bool min_in_range = T::min_in_range;
+    constexpr bool max_in_range = T::max_in_range;
+
+    type const val_min = std::numeric_limits<type>::min();
+    type const val_min2 = val_min + 1;
+    type const val_max = std::numeric_limits<type>::max();
+    type const val_max2 = val_max - 1;
+
+    REQUIRE(CHAR_BIT == 8);
+
+    std::string of_type_str;
+    if (std::is_unsigned<of_type>::value)
+    {
+        of_type_str += "u";
+    }
+    of_type_str += "int";
+    of_type_str += std::to_string(sizeof(of_type) * 8);
+
+    INFO("of_type := ", of_type_str);
+
+    std::string type_str;
+    if (std::is_unsigned<type>::value)
+    {
+        type_str += "u";
+    }
+    type_str += "int";
+    type_str += std::to_string(sizeof(type) * 8);
+
+    INFO("type := ", type_str);
+
+    CAPTURE(val_min);
+    CAPTURE(min_in_range);
+    CAPTURE(val_max);
+    CAPTURE(max_in_range);
+
+    if (min_in_range)
+    {
+        CHECK(value_in_range_of<of_type>(val_min));
+        CHECK(value_in_range_of<of_type>(val_min2));
+    }
+    else
+    {
+        CHECK_FALSE(value_in_range_of<of_type>(val_min));
+        CHECK_FALSE(value_in_range_of<of_type>(val_min2));
+    }
+
+    if (max_in_range)
+    {
+        CHECK(value_in_range_of<of_type>(val_max));
+        CHECK(value_in_range_of<of_type>(val_max2));
+    }
+    else
+    {
+        CHECK_FALSE(value_in_range_of<of_type>(val_max));
+        CHECK_FALSE(value_in_range_of<of_type>(val_max2));
+    }
+}