Fix test lints that are red on develop (effc++, clang-tidy) (#5946)

- unit-bson: initialize the SAX recorder's member (-Weffc++)
- unit-json_patch: build the reference document independently instead of
  copying it (performance-unnecessary-copy-initialization)
- unit-json_view_builder: use node_kind::link instead of an out-of-range
  enum cast (clang-analyzer-optin.core.EnumCastOutOfRange)

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

tests/src/unit-bson.cpp

@@ -1311,7 +1311,7 @@ TEST_CASE("BSON declared document size bounds the content")
     // records the events that a SAX parser receives
     struct recorder : nlohmann::json_sax<json>
     {
-        std::string events;
+        std::string events {};
 
         bool null() override
         {

tests/src/unit-json_patch.cpp

@@ -2178,8 +2178,13 @@ TEST_CASE("JSON patch - behavior documented in the API reference")
 
     SECTION("patch() has the strong guarantee")
     {
-        const json doc = R"({"a": [1, 2], "o": {"k": "v"}})"_json;
+        // independent values, so that the comparison below checks the untouched document
-        const json before = doc;
+        const auto make_doc = []
+        {
+            return R"({"a": [1, 2], "o": {"k": "v"}})"_json;
+        };
+        const json doc = make_doc();
+        const json before = make_doc();
 
         const std::vector<json> failing =
         {
@@ -2202,7 +2207,7 @@ TEST_CASE("JSON patch - behavior documented in the API reference")
             CHECK_THROWS_AS(doc.patch(patch), json::exception&);
             CHECK(doc == before);
 
-            json copy = doc;
+            json copy = make_doc();
             CHECK_THROWS_AS(copy.patch(patch), json::exception&);
             CHECK(copy == before);
         }

tests/src/unit-json_view_builder.cpp

@@ -592,7 +592,7 @@ TEST_CASE("json_view node integer bits")
                 })
         {
             CAPTURE(v)
-            n.kind = static_cast<nlohmann::detail::view::node_kind>(0x5A);
+            n.kind = nlohmann::detail::view::node_kind::link;
             n.flags = 0xA5;
             n.extra = 0x1234;
             n.off = 0x89ABCDEFu;
@@ -601,7 +601,7 @@ TEST_CASE("json_view node integer bits")
             CHECK(n.len == static_cast<std::uint32_t>(v));
             CHECK(n.next == static_cast<std::uint32_t>(v >> 32));
             // the other fields are untouched
-            CHECK(static_cast<std::uint8_t>(n.kind) == 0x5A);
+            CHECK(n.kind == nlohmann::detail::view::node_kind::link);
             CHECK(n.flags == 0xA5);
             CHECK(n.extra == 0x1234);
             CHECK(n.off == 0x89ABCDEFu);