Tests: cover the remaining lines of the library headers

Add tests for the lines of include/nlohmann that were not covered: the
binary readers and writers, the lexer and locale paths, the json_view
modules, the custom number, key and array types, json_pointer, json_patch,
diff and the iterators.

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

tests/src/unit-stream-bulk-scan.cpp

@@ -19,11 +19,13 @@
 using nlohmann::json;
 
 #include <algorithm>
+#include <array>
 #include <cstddef>
 #include <cstdint>
 #include <cstdio>
 #include <fstream>
 #include <istream>
+#include <limits>
 #include <random>
 #include <sstream>
 #include <streambuf>
@@ -93,6 +95,25 @@ class chunked_streambuf : public std::streambuf
     std::size_t m_unbuffered;
 };
 
+#if TEST_STREAM_BULK_SCAN
+// A streambuf that claims a get area of several gigabytes, of which only the
+// first bytes exist. It is only used to move the read position of the adapter,
+// never to read beyond them, so that skipping more than gbump() can bump at
+// once can be tested without allocating that much.
+class oversized_get_area_streambuf : public std::streambuf
+{
+  public:
+    explicit oversized_get_area_streambuf(std::size_t claimed_size)
+    {
+        // NOLINTNEXTLINE(cppcoreguidelines-pro-bounds-pointer-arithmetic)
+        setg(m_data.data(), m_data.data(), m_data.data() + claimed_size);
+    }
+
+  private:
+    std::array<char, 8> m_data{{'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'}};
+};
+#endif
+
 // how a test reads from the stream
 enum class read_mode
 {
@@ -433,6 +454,31 @@ TEST_CASE("parsing from a std::istream scans the get area in bulk")
         ia.copy_token(token, false);
         CHECK(token.empty());
     }
+
+    SECTION("skipping more characters than gbump() takes at once")
+    {
+        // gbump() takes an int, but a get area can be larger
+        if (sizeof(std::size_t) < 8)
+        {
+            MESSAGE("a get area larger than an int needs a 64-bit size_t");
+        }
+        else
+        {
+            const std::size_t claimed = std::size_t{3} << 30u;
+            oversized_get_area_streambuf buf(claimed);
+            std::istream is(&buf);
+            nlohmann::detail::input_stream_adapter ia(is);
+            CHECK(ia.get_character() == 'a');
+            CHECK(ia.bulk_remaining() == claimed - 1);
+
+            const std::size_t skipped = static_cast<std::size_t>((std::numeric_limits<int>::max)()) + 10;
+            ia.bulk_skip(skipped);
+            CHECK(ia.bulk_remaining() == claimed - 1 - skipped);
+
+            ia.bulk_skip(ia.bulk_remaining());
+            CHECK(ia.bulk_remaining() == 0);
+        }
+    }
 #endif
 
     SECTION("SAX parsing from a stream")