diff --git a/include/nlohmann/detail/input/binary_reader.hpp b/include/nlohmann/detail/input/binary_reader.hpp
index 634615d35..1fb1c052b 100644
--- a/include/nlohmann/detail/input/binary_reader.hpp
+++ b/include/nlohmann/detail/input/binary_reader.hpp
@@ -330,7 +330,7 @@ class binary_reader
             {
                 std::array<char, 3> cr{{}};
                 static_cast<void>((std::snprintf)(cr.data(), cr.size(), "%.2hhX", static_cast<unsigned char>(element_type))); // NOLINT(cppcoreguidelines-pro-type-vararg,hicpp-vararg)
-                std::string cr_str{cr.data()};
+                const std::string cr_str{cr.data()};
                 return sax->parse_error(element_type_parse_position, cr_str,
                                         parse_error::create(114, element_type_parse_position, concat("Unsupported BSON record type 0x", cr_str), nullptr));
             }
@@ -2265,7 +2265,7 @@ class binary_reader
                                         exception_message(input_format, concat("expected '#' after type information; last byte: 0x", last_token), "size"), nullptr));
             }
 
-            bool is_error = get_ubjson_size_value(result.first, is_ndarray);
+            const bool is_error = get_ubjson_size_value(result.first, is_ndarray);
             if (input_format == input_format_t::bjdata && is_ndarray)
             {
                 if (inside_ndarray)
@@ -2280,7 +2280,7 @@ class binary_reader
 
         if (current == '#')
         {
-            bool is_error = get_ubjson_size_value(result.first, is_ndarray);
+            const bool is_error = get_ubjson_size_value(result.first, is_ndarray);
             if (input_format == input_format_t::bjdata && is_ndarray)
             {
                 return sax->parse_error(chars_read, get_token_string(), parse_error::create(112, chars_read,
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 7a2f9dabb..40e84d43f 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -9408,7 +9408,7 @@ class binary_reader
             {
                 std::array<char, 3> cr{{}};
                 static_cast<void>((std::snprintf)(cr.data(), cr.size(), "%.2hhX", static_cast<unsigned char>(element_type))); // NOLINT(cppcoreguidelines-pro-type-vararg,hicpp-vararg)
-                std::string cr_str{cr.data()};
+                const std::string cr_str{cr.data()};
                 return sax->parse_error(element_type_parse_position, cr_str,
                                         parse_error::create(114, element_type_parse_position, concat("Unsupported BSON record type 0x", cr_str), nullptr));
             }
@@ -11343,7 +11343,7 @@ class binary_reader
                                         exception_message(input_format, concat("expected '#' after type information; last byte: 0x", last_token), "size"), nullptr));
             }
 
-            bool is_error = get_ubjson_size_value(result.first, is_ndarray);
+            const bool is_error = get_ubjson_size_value(result.first, is_ndarray);
             if (input_format == input_format_t::bjdata && is_ndarray)
             {
                 if (inside_ndarray)
@@ -11358,7 +11358,7 @@ class binary_reader
 
         if (current == '#')
         {
-            bool is_error = get_ubjson_size_value(result.first, is_ndarray);
+            const bool is_error = get_ubjson_size_value(result.first, is_ndarray);
             if (input_format == input_format_t::bjdata && is_ndarray)
             {
                 return sax->parse_error(chars_read, get_token_string(), parse_error::create(112, chars_read,
diff --git a/tests/abi/config/custom.cpp b/tests/abi/config/custom.cpp
index a004fcca2..87d3aa6ea 100644
--- a/tests/abi/config/custom.cpp
+++ b/tests/abi/config/custom.cpp
@@ -25,7 +25,7 @@ TEST_CASE("custom namespace")
         std::string expected = "nlohmann::basic_json";
 
         // fallback for Clang
-        std::string ns{STRINGIZE(NLOHMANN_JSON_NAMESPACE) "::basic_json"};
+        const std::string ns{STRINGIZE(NLOHMANN_JSON_NAMESPACE) "::basic_json"};
 
         CHECK(namespace_name<nlohmann::json>(ns) == expected);
     }
diff --git a/tests/abi/config/default.cpp b/tests/abi/config/default.cpp
index 908314acf..51bf0c3bb 100644
--- a/tests/abi/config/default.cpp
+++ b/tests/abi/config/default.cpp
@@ -33,7 +33,7 @@ TEST_CASE("default namespace")
         expected += "_" STRINGIZE(NLOHMANN_JSON_VERSION_PATCH) "::basic_json";
 
         // fallback for Clang
-        std::string ns{STRINGIZE(NLOHMANN_JSON_NAMESPACE) "::basic_json"};
+        const std::string ns{STRINGIZE(NLOHMANN_JSON_NAMESPACE) "::basic_json"};
 
         CHECK(namespace_name<nlohmann::json>(ns) == expected);
     }
diff --git a/tests/abi/config/noversion.cpp b/tests/abi/config/noversion.cpp
index d4fcb3f46..e6b4f7721 100644
--- a/tests/abi/config/noversion.cpp
+++ b/tests/abi/config/noversion.cpp
@@ -32,7 +32,7 @@ TEST_CASE("default namespace without version component")
         expected += "::basic_json";
 
         // fallback for Clang
-        std::string ns{STRINGIZE(NLOHMANN_JSON_NAMESPACE) "::basic_json"};
+        const std::string ns{STRINGIZE(NLOHMANN_JSON_NAMESPACE) "::basic_json"};
 
         CHECK(namespace_name<nlohmann::json>(ns) == expected);
     }
diff --git a/tests/src/unit-comparison.cpp b/tests/src/unit-comparison.cpp
index b838c02f2..7f990d252 100644
--- a/tests/src/unit-comparison.cpp
+++ b/tests/src/unit-comparison.cpp
@@ -391,7 +391,7 @@ TEST_CASE("lexicographical comparison operators")
             }
 
             // compare with null pointer
-            json j_null;
+            const json j_null;
             CHECK((j_null != nullptr) == false);
             CHECK((nullptr != j_null) == false);
             CHECK((j_null != nullptr) == !(j_null == nullptr));
diff --git a/tests/src/unit-concepts.cpp b/tests/src/unit-concepts.cpp
index 3a0c81b05..e96caba7e 100644
--- a/tests/src/unit-concepts.cpp
+++ b/tests/src/unit-concepts.cpp
@@ -57,7 +57,7 @@ TEST_CASE("concepts")
 
         // the expression "X u" has the post-condition "u.empty()"
         {
-            json u;
+            const json u;
             CHECK(u.empty());
         }
 
diff --git a/tests/src/unit-conversions.cpp b/tests/src/unit-conversions.cpp
index 78ed3bb3e..24d89e11a 100644
--- a/tests/src/unit-conversions.cpp
+++ b/tests/src/unit-conversions.cpp
@@ -36,7 +36,7 @@ TEST_CASE("value conversion")
 {
     SECTION("get an object (explicit)")
     {
-        json::object_t o_reference = {{"object", json::object()},
+        const json::object_t o_reference = {{"object", json::object()},
             {"array", {1, 2, 3, 4}},
             {"number", 42},
             {"boolean", false},
@@ -53,28 +53,28 @@ TEST_CASE("value conversion")
 
         SECTION("std::map<json::string_t, json>")
         {
-            std::map<json::string_t, json> o =
+            const std::map<json::string_t, json> o =
                 j.get<std::map<json::string_t, json>>();
             CHECK(json(o) == j);
         }
 
         SECTION("std::multimap<json::string_t, json>")
         {
-            std::multimap<json::string_t, json> o =
+            const std::multimap<json::string_t, json> o =
                 j.get<std::multimap<json::string_t, json>>();
             CHECK(json(o) == j);
         }
 
         SECTION("std::unordered_map<json::string_t, json>")
         {
-            std::unordered_map<json::string_t, json> o =
+            const std::unordered_map<json::string_t, json> o =
                 j.get<std::unordered_map<json::string_t, json>>();
             CHECK(json(o) == j);
         }
 
         SECTION("std::unordered_multimap<json::string_t, json>")
         {
-            std::unordered_multimap<json::string_t, json> o =
+            const std::unordered_multimap<json::string_t, json> o =
                 j.get<std::unordered_multimap<json::string_t, json>>();
             CHECK(json(o) == j);
         }
@@ -107,7 +107,7 @@ TEST_CASE("value conversion")
 
     SECTION("get an object (explicit, get_to)")
     {
-        json::object_t o_reference = {{"object", json::object()},
+        const json::object_t o_reference = {{"object", json::object()},
             {"array", {1, 2, 3, 4}},
             {"number", 42},
             {"boolean", false},
@@ -155,7 +155,7 @@ TEST_CASE("value conversion")
 #if JSON_USE_IMPLICIT_CONVERSIONS
     SECTION("get an object (implicit)")
     {
-        json::object_t o_reference = {{"object", json::object()},
+        const json::object_t o_reference = {{"object", json::object()},
             {"array", {1, 2, 3, 4}},
             {"number", 42},
             {"boolean", false},
@@ -166,31 +166,31 @@ TEST_CASE("value conversion")
 
         SECTION("json::object_t")
         {
-            json::object_t o = j;
+            const json::object_t o = j;
             CHECK(json(o) == j);
         }
 
         SECTION("std::map<json::string_t, json>")
         {
-            std::map<json::string_t, json> o = j;
+            const std::map<json::string_t, json> o = j;
             CHECK(json(o) == j);
         }
 
         SECTION("std::multimap<json::string_t, json>")
         {
-            std::multimap<json::string_t, json> o = j;
+            const std::multimap<json::string_t, json> o = j;
             CHECK(json(o) == j);
         }
 
         SECTION("std::unordered_map<json::string_t, json>")
         {
-            std::unordered_map<json::string_t, json> o = j;
+            const std::unordered_map<json::string_t, json> o = j;
             CHECK(json(o) == j);
         }
 
         SECTION("std::unordered_multimap<json::string_t, json>")
         {
-            std::unordered_multimap<json::string_t, json> o = j;
+            const std::unordered_multimap<json::string_t, json> o = j;
             CHECK(json(o) == j);
         }
     }
@@ -198,25 +198,25 @@ TEST_CASE("value conversion")
 
     SECTION("get an array (explicit)")
     {
-        json::array_t a_reference{json(1),     json(1u),       json(2.2),
-                                  json(false), json("string"), json()};
+        const json::array_t a_reference{json(1),     json(1u),       json(2.2),
+                                        json(false), json("string"), json()};
         json j(a_reference);
 
         SECTION("json::array_t")
         {
-            json::array_t a = j.get<json::array_t>();
+            const json::array_t a = j.get<json::array_t>();
             CHECK(json(a) == j);
         }
 
         SECTION("std::list<json>")
         {
-            std::list<json> a = j.get<std::list<json>>();
+            const std::list<json> a = j.get<std::list<json>>();
             CHECK(json(a) == j);
         }
 
         SECTION("std::forward_list<json>")
         {
-            std::forward_list<json> a = j.get<std::forward_list<json>>();
+            const std::forward_list<json> a = j.get<std::forward_list<json>>();
             CHECK(json(a) == j);
 
             CHECK_THROWS_WITH_AS(
@@ -226,7 +226,7 @@ TEST_CASE("value conversion")
 
         SECTION("std::vector<json>")
         {
-            std::vector<json> a = j.get<std::vector<json>>();
+            const std::vector<json> a = j.get<std::vector<json>>();
             CHECK(json(a) == j);
 
             CHECK_THROWS_WITH_AS(
@@ -237,7 +237,7 @@ TEST_CASE("value conversion")
             SECTION("reserve is called on containers that supports it")
             {
                 // make sure all values are properly copied
-                json j2({1, 2, 3, 4, 5, 6, 7, 8, 9, 10});
+                const json j2({1, 2, 3, 4, 5, 6, 7, 8, 9, 10});
                 auto v2 = j2.get<std::vector<int>>();
                 CHECK(v2.size() == 10);
             }
@@ -249,8 +249,8 @@ TEST_CASE("value conversion")
             const char str[] = "a string"; // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
             const int nbs[] = {0, 1, 2}; // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
 
-            json j2 = nbs;
-            json j3 = str;
+            const json j2 = nbs;
+            const json j3 = str;
 
             auto v = j2.get<std::vector<int>>();
             auto s = j3.get<std::string>();
@@ -260,7 +260,7 @@ TEST_CASE("value conversion")
 
         SECTION("std::deque<json>")
         {
-            std::deque<json> a = j.get<std::deque<json>>();
+            const std::deque<json> a = j.get<std::deque<json>>();
             CHECK(json(a) == j);
         }
 
@@ -295,8 +295,8 @@ TEST_CASE("value conversion")
 
     SECTION("get an array (explicit, get_to)")
     {
-        json::array_t a_reference{json(1),     json(1u),       json(2.2),
-                                  json(false), json("string"), json()};
+        const json::array_t a_reference{json(1),     json(1u),       json(2.2),
+                                        json(false), json("string"), json()};
         json j(a_reference);
 
         SECTION("json::array_t")
@@ -339,7 +339,7 @@ TEST_CASE("value conversion")
             const int nbs[] = {0, 1, 2}; // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
             int nbs2[] = {0, 0, 0}; // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
 
-            json j2 = nbs;
+            const json j2 = nbs;
             j2.get_to(nbs2);
             CHECK(std::equal(std::begin(nbs), std::end(nbs), std::begin(nbs2)));
         }
@@ -355,37 +355,37 @@ TEST_CASE("value conversion")
 #if JSON_USE_IMPLICIT_CONVERSIONS
     SECTION("get an array (implicit)")
     {
-        json::array_t a_reference{json(1),     json(1u),       json(2.2),
-                                  json(false), json("string"), json()};
+        const json::array_t a_reference{json(1),     json(1u),       json(2.2),
+                                        json(false), json("string"), json()};
         json j(a_reference);
 
         SECTION("json::array_t")
         {
-            json::array_t a = j;
+            const json::array_t a = j;
             CHECK(json(a) == j);
         }
 
         SECTION("std::list<json>")
         {
-            std::list<json> a = j;
+            const std::list<json> a = j;
             CHECK(json(a) == j);
         }
 
         SECTION("std::forward_list<json>")
         {
-            std::forward_list<json> a = j;
+            const std::forward_list<json> a = j;
             CHECK(json(a) == j);
         }
 
         SECTION("std::vector<json>")
         {
-            std::vector<json> a = j;
+            const std::vector<json> a = j;
             CHECK(json(a) == j);
         }
 
         SECTION("std::deque<json>")
         {
-            std::deque<json> a = j;
+            const std::deque<json> a = j;
             CHECK(json(a) == j);
         }
     }
@@ -393,18 +393,18 @@ TEST_CASE("value conversion")
 
     SECTION("get a string (explicit)")
     {
-        json::string_t s_reference{"Hello world"};
+        const json::string_t s_reference{"Hello world"};
         json j(s_reference);
 
         SECTION("string_t")
         {
-            json::string_t s = j.get<json::string_t>();
+            const json::string_t s = j.get<json::string_t>();
             CHECK(json(s) == j);
         }
 
         SECTION("std::string")
         {
-            std::string s = j.get<std::string>();
+            const std::string s = j.get<std::string>();
             CHECK(json(s) == j);
         }
 #if defined(JSON_HAS_CPP_17)
@@ -463,7 +463,7 @@ TEST_CASE("value conversion")
 
     SECTION("get a string (explicit, get_to)")
     {
-        json::string_t s_reference{"Hello world"};
+        const json::string_t s_reference{"Hello world"};
         json j(s_reference);
 
         SECTION("string_t")
@@ -493,7 +493,7 @@ TEST_CASE("value conversion")
     SECTION("get null (explicit)")
     {
         std::nullptr_t n = nullptr;
-        json j(n);
+        const json j(n);
 
         auto n2 = j.get<std::nullptr_t>();
         CHECK(n2 == n);
@@ -517,12 +517,12 @@ TEST_CASE("value conversion")
 #if JSON_USE_IMPLICIT_CONVERSIONS
     SECTION("get a string (implicit)")
     {
-        json::string_t s_reference{"Hello world"};
+        const json::string_t s_reference{"Hello world"};
         json j(s_reference);
 
         SECTION("string_t")
         {
-            json::string_t s = j;
+            const json::string_t s = j;
             CHECK(json(s) == j);
         }
 
@@ -536,7 +536,7 @@ TEST_CASE("value conversion")
 
         SECTION("std::string")
         {
-            std::string s = j;
+            const std::string s = j;
             CHECK(json(s) == j);
         }
     }
@@ -544,7 +544,7 @@ TEST_CASE("value conversion")
 
     SECTION("get a boolean (explicit)")
     {
-        json::boolean_t b_reference{true};
+        const json::boolean_t b_reference{true};
         json j(b_reference);
 
         SECTION("boolean_t")
@@ -561,7 +561,7 @@ TEST_CASE("value conversion")
 
         SECTION("bool")
         {
-            bool b = j.get<bool>();
+            const bool b = j.get<bool>();
             CHECK(json(b) == j);
         }
 
@@ -600,18 +600,18 @@ TEST_CASE("value conversion")
 #if JSON_USE_IMPLICIT_CONVERSIONS
     SECTION("get a boolean (implicit)")
     {
-        json::boolean_t b_reference{true};
+        const json::boolean_t b_reference{true};
         json j(b_reference);
 
         SECTION("boolean_t")
         {
-            json::boolean_t b = j;
+            const json::boolean_t b = j;
             CHECK(json(b) == j);
         }
 
         SECTION("bool")
         {
-            bool b = j;
+            const bool b = j;
             CHECK(json(b) == j);
         }
     }
@@ -619,9 +619,9 @@ TEST_CASE("value conversion")
 
     SECTION("get an integer number (explicit)")
     {
-        json::number_integer_t n_reference{42};
+        const json::number_integer_t n_reference{42};
         json j(n_reference);
-        json::number_unsigned_t n_unsigned_reference{42u};
+        const json::number_unsigned_t n_unsigned_reference{42u};
         json j_unsigned(n_unsigned_reference);
 
         SECTION("number_integer_t")
@@ -650,7 +650,7 @@ TEST_CASE("value conversion")
 
         SECTION("int")
         {
-            int n = j.get<int>();
+            const int n = j.get<int>();
             CHECK(json(n) == j);
         }
 
@@ -662,7 +662,7 @@ TEST_CASE("value conversion")
 
         SECTION("long")
         {
-            long n = j.get<long>();
+            const long n = j.get<long>();
             CHECK(json(n) == j);
         }
 
diff --git a/tests/src/unit-reference_access.cpp b/tests/src/unit-reference_access.cpp
index 5f450ec2c..32a4097dd 100644
--- a/tests/src/unit-reference_access.cpp
+++ b/tests/src/unit-reference_access.cpp
@@ -14,7 +14,7 @@ using nlohmann::json;
 TEST_CASE("reference access")
 {
     // create a JSON value with different types
-    json json_types =
+    const json json_types =
     {
         {"boolean", true},
         {
diff --git a/tests/src/unit-regression2.cpp b/tests/src/unit-regression2.cpp
index 503d2a4f8..308ceeef9 100644
--- a/tests/src/unit-regression2.cpp
+++ b/tests/src/unit-regression2.cpp
@@ -348,7 +348,7 @@ TEST_CASE("regression tests 2")
                ]
              })";
 
-        json::parser_callback_t cb = [&](int /*level*/, json::parse_event_t event, json & parsed) noexcept
+        const json::parser_callback_t cb = [&](int /*level*/, json::parse_event_t event, json & parsed) noexcept
         {
             // skip uninteresting events
             if (event == json::parse_event_t::value && !parsed.is_primitive())
@@ -440,7 +440,7 @@ TEST_CASE("regression tests 2")
     SECTION("issue #1299 - compile error in from_json converting to container "
             "with std::pair")
     {
-        json j =
+        const json j =
         {
             {"1", {{"a", "testa_1"}, {"b", "testb_1"}}},
             {"2", {{"a", "testa_2"}, {"b", "testb_2"}}},
@@ -501,7 +501,7 @@ TEST_CASE("regression tests 2")
                 {109, 108, 103, 125, -122, -53, 115, 18, 3, 0, 102, 19, 1, 15, -110, 13, -3, -1, -81, 32, 2, 0, 0, 0, 0, 0, 0, 0, 8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, -80, 2, 0, 0, 96, -118, 46, -116, 46, 109, -84, -87, 108, 14, 109, -24, -83, 13, -18, -51, -83, -52, -115, 14, 6, 32, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 64, 3, 0, 0, 0, 35, -74, -73, 55, 57, -128, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 33, 0, 0, 0, -96, -54, -28, -26}
             };
             std::string s;
-            for (int i : data)
+            for (const int i : data)
             {
                 s += static_cast<char>(i);
             }
@@ -512,20 +512,20 @@ TEST_CASE("regression tests 2")
 
     SECTION("issue #1447 - Integer Overflow (OSS-Fuzz 12506)")
     {
-        json j = json::parse("[-9223372036854775808]");
+        const json j = json::parse("[-9223372036854775808]");
         CHECK(j.dump() == "[-9223372036854775808]");
     }
 
     SECTION("issue #1708 - minimum value of int64_t can be outputted")
     {
         constexpr auto smallest = (std::numeric_limits<int64_t>::min)();
-        json j = smallest;
+        const json j = smallest;
         CHECK(j.dump() == std::to_string(smallest));
     }
 
     SECTION("issue #1727 - Contains with non-const lvalue json_pointer picks the wrong overload")
     {
-        json j = {{"root", {{"settings", {{"logging", true}}}}}};
+        const json j = {{"root", {{"settings", {{"logging", true}}}}}};
 
         auto jptr1 = "/root/settings/logging"_json_pointer;
         auto jptr2 = json::json_pointer{"/root/settings/logging"};
@@ -539,7 +539,7 @@ TEST_CASE("regression tests 2")
         // does not compile on ICPC when targeting C++20
 #if !(defined(__INTEL_COMPILER) && __cplusplus >= 202000)
         {
-            json j;
+            const json j;
             NonDefaultFromJsonStruct x(j);
             NonDefaultFromJsonStruct y;
             CHECK(x == y);
@@ -548,27 +548,27 @@ TEST_CASE("regression tests 2")
 
         auto val = nlohmann::json("one").get<for_1647>();
         CHECK(val == for_1647::one);
-        json j = val;
+        const json j = val;
     }
 
     SECTION("issue #1715 - json::from_cbor does not respect allow_exceptions = false when input is string literal")
     {
         SECTION("string literal")
         {
-            json cbor = json::from_cbor("B", true, false);
+            const json cbor = json::from_cbor("B", true, false);
             CHECK(cbor.is_discarded());
         }
 
         SECTION("string array")
         {
             const std::array<char, 2> input = {{'B', 0x00}};
-            json cbor = json::from_cbor(input, true, false);
+            const json cbor = json::from_cbor(input, true, false);
             CHECK(cbor.is_discarded());
         }
 
         SECTION("std::string")
         {
-            json cbor = json::from_cbor(std::string("B"), true, false);
+            const json cbor = json::from_cbor(std::string("B"), true, false);
             CHECK(cbor.is_discarded());
         }
     }
@@ -597,7 +597,7 @@ TEST_CASE("regression tests 2")
     SECTION("issue #2067 - cannot serialize binary data to text JSON")
     {
         const std::array<unsigned char, 23> data = {{0x81, 0xA4, 0x64, 0x61, 0x74, 0x61, 0xC4, 0x0F, 0x33, 0x30, 0x30, 0x32, 0x33, 0x34, 0x30, 0x31, 0x30, 0x37, 0x30, 0x35, 0x30, 0x31, 0x30}};
-        json j = json::from_msgpack(data.data(), data.size());
+        const json j = json::from_msgpack(data.data(), data.size());
         CHECK_NOTHROW(
             j.dump(4,                             // Indent
                    ' ',                           // Indent char
@@ -609,15 +609,15 @@ TEST_CASE("regression tests 2")
     SECTION("PR #2181 - regression bug with lvalue")
     {
         // see https://github.com/nlohmann/json/pull/2181#issuecomment-653326060
-        json j{{"x", "test"}};
-        std::string defval = "default value";
+        const json j{{"x", "test"}};
+        const std::string defval = "default value";
         auto val = j.value("x", defval);
         auto val2 = j.value("y", defval);
     }
 
     SECTION("issue #2293 - eof doesn't cause parsing to stop")
     {
-        std::vector<uint8_t> data =
+        const std::vector<uint8_t> data =
         {
             0x7B,
             0x6F,
@@ -630,23 +630,23 @@ TEST_CASE("regression tests 2")
             0x4F,
             0x42
         };
-        json result = json::from_cbor(data, true, false);
+        const json result = json::from_cbor(data, true, false);
         CHECK(result.is_discarded());
     }
 
     SECTION("issue #2315 - json.update and vector<pair>does not work with ordered_json")
     {
         nlohmann::ordered_json jsonAnimals = {{"animal", "dog"}};
-        nlohmann::ordered_json jsonCat = {{"animal", "cat"}};
+        const nlohmann::ordered_json jsonCat = {{"animal", "cat"}};
         jsonAnimals.update(jsonCat);
         CHECK(jsonAnimals["animal"] == "cat");
 
         auto jsonAnimals_parsed = nlohmann::ordered_json::parse(jsonAnimals.dump());
         CHECK(jsonAnimals == jsonAnimals_parsed);
 
-        std::vector<std::pair<std::string, int64_t>> intData = {std::make_pair("aaaa", 11),
-                                                                std::make_pair("bbb", 222)
-                                                               };
+        const std::vector<std::pair<std::string, int64_t>> intData = {std::make_pair("aaaa", 11),
+                                                                      std::make_pair("bbb", 222)
+                                                                     };
         nlohmann::ordered_json jsonObj;
         for (const auto& data : intData)
         {
@@ -658,8 +658,8 @@ TEST_CASE("regression tests 2")
 
     SECTION("issue #2330 - ignore_comment=true fails on multiple consecutive lines starting with comments")
     {
-        std::string ss = "//\n//\n{\n}\n";
-        json j = json::parse(ss, nullptr, true, true);
+        const std::string ss = "//\n//\n{\n}\n";
+        const json j = json::parse(ss, nullptr, true, true);
         CHECK(j.dump() == "{}");
     }
 
@@ -668,7 +668,7 @@ TEST_CASE("regression tests 2")
     {
         const char DATA[] = R"("Hello, world!")"; // NOLINT(cppcoreguidelines-avoid-c-arrays,hicpp-avoid-c-arrays,modernize-avoid-c-arrays)
         const auto s = std::as_bytes(std::span(DATA));
-        json j = json::parse(s);
+        const json j = json::parse(s);
         CHECK(j.dump() == "\"Hello, world!\"");
     }
 #endif
@@ -678,14 +678,14 @@ TEST_CASE("regression tests 2")
         SECTION("std::array")
         {
             {
-                json j = {7, 4};
+                const json j = {7, 4};
                 auto arr = j.get<std::array<NonDefaultConstructible, 2>>();
                 CHECK(arr[0].x == 7);
                 CHECK(arr[1].x == 4);
             }
 
             {
-                json j = 7;
+                const json j = 7;
                 CHECK_THROWS_AS((j.get<std::array<NonDefaultConstructible, 1>>()), json::type_error);
             }
         }
@@ -693,28 +693,28 @@ TEST_CASE("regression tests 2")
         SECTION("std::pair")
         {
             {
-                json j = {3, 8};
+                const json j = {3, 8};
                 auto p = j.get<std::pair<NonDefaultConstructible, NonDefaultConstructible>>();
                 CHECK(p.first.x == 3);
                 CHECK(p.second.x == 8);
             }
 
             {
-                json j = {4, 1};
+                const json j = {4, 1};
                 auto p = j.get<std::pair<int, NonDefaultConstructible>>();
                 CHECK(p.first == 4);
                 CHECK(p.second.x == 1);
             }
 
             {
-                json j = {6, 7};
+                const json j = {6, 7};
                 auto p = j.get<std::pair<NonDefaultConstructible, int>>();
                 CHECK(p.first.x == 6);
                 CHECK(p.second == 7);
             }
 
             {
-                json j = 7;
+                const json j = 7;
                 CHECK_THROWS_AS((j.get<std::pair<NonDefaultConstructible, int>>()), json::type_error);
             }
         }
@@ -722,13 +722,13 @@ TEST_CASE("regression tests 2")
         SECTION("std::tuple")
         {
             {
-                json j = {9};
+                const json j = {9};
                 auto t = j.get<std::tuple<NonDefaultConstructible>>();
                 CHECK(std::get<0>(t).x == 9);
             }
 
             {
-                json j = {9, 8, 7};
+                const json j = {9, 8, 7};
                 auto t = j.get<std::tuple<NonDefaultConstructible, int, NonDefaultConstructible>>();
                 CHECK(std::get<0>(t).x == 9);
                 CHECK(std::get<1>(t) == 8);
@@ -736,7 +736,7 @@ TEST_CASE("regression tests 2")
             }
 
             {
-                json j = 7;
+                const json j = 7;
                 CHECK_THROWS_AS((j.get<std::tuple<NonDefaultConstructible>>()), json::type_error);
             }
         }
@@ -747,7 +747,7 @@ TEST_CASE("regression tests 2")
         // the code below is expected to not leak memory
         {
             nlohmann::json o;
-            std::string s = "bar";
+            const std::string s = "bar";
 
             nlohmann::to_json(o["foo"], s);
 
@@ -759,7 +759,7 @@ TEST_CASE("regression tests 2")
 
         {
             nlohmann::json o;
-            std::string s = "bar";
+            const std::string s = "bar";
 
             nlohmann::to_json(o["foo"], s);
 
@@ -785,7 +785,7 @@ TEST_CASE("regression tests 2")
 
     SECTION("issue #2958 - Inserting in unordered json using a pointer retains the leading slash")
     {
-        std::string p = "/root";
+        const std::string p = "/root";
 
         json test1;
         test1[json::json_pointer(p)] = json::object();
@@ -816,7 +816,7 @@ TEST_CASE("regression tests 2")
     SECTION("issue #3070 - Version 3.10.3 breaks backward-compatibility with 3.10.2 ")
     {
         nlohmann::detail::std_fs::path text_path("/tmp/text.txt");
-        json j(text_path);
+        const json j(text_path);
 
         const auto j_path = j.get<nlohmann::detail::std_fs::path>();
         CHECK(j_path == text_path);
@@ -867,7 +867,7 @@ TEST_CASE("regression tests 2")
 
     SECTION("issue #3171 - if class is_constructible from std::string wrong from_json overload is being selected, compilation failed")
     {
-        json j{{ "str", "value"}};
+        const json j{{ "str", "value"}};
 
         // failed with: error: no match for ‘operator=’ (operand types are ‘for_3171_derived’ and ‘const nlohmann::basic_json<>::string_t’
         //                                               {aka ‘const std::__cxx11::basic_string<char>’})
@@ -881,7 +881,7 @@ TEST_CASE("regression tests 2")
     SECTION("issue #3312 - Parse to custom class from unordered_json breaks on G++11.2.0 with C++20")
     {
         // see test for #3171
-        ordered_json j = {{"name", "class"}};
+        const ordered_json j = {{"name", "class"}};
         for_3312 obj{};
 
         j.get_to(obj);
@@ -893,8 +893,8 @@ TEST_CASE("regression tests 2")
 #if defined(JSON_HAS_CPP_17) && JSON_USE_IMPLICIT_CONVERSIONS
     SECTION("issue #3428 - Error occurred when converting nlohmann::json to std::any")
     {
-        json j;
-        std::any a1 = j;
+        const json j;
+        const std::any a1 = j;
         std::any&& a2 = j;
 
         CHECK(a1.type() == typeid(j));
diff --git a/tests/src/unit-serialization.cpp b/tests/src/unit-serialization.cpp
index a023d23d9..01e5bdfea 100644
--- a/tests/src/unit-serialization.cpp
+++ b/tests/src/unit-serialization.cpp
@@ -21,7 +21,7 @@ TEST_CASE("serialization")
         SECTION("no given width")
         {
             std::stringstream ss;
-            json j = {"foo", 1, 2, 3, false, {{"one", 1}}};
+            const json j = {"foo", 1, 2, 3, false, {{"one", 1}}};
             ss << j;
             CHECK(ss.str() == "[\"foo\",1,2,3,false,{\"one\":1}]");
         }
@@ -29,7 +29,7 @@ TEST_CASE("serialization")
         SECTION("given width")
         {
             std::stringstream ss;
-            json j = {"foo", 1, 2, 3, false, {{"one", 1}}};
+            const json j = {"foo", 1, 2, 3, false, {{"one", 1}}};
             ss << std::setw(4) << j;
             CHECK(ss.str() ==
                   "[\n    \"foo\",\n    1,\n    2,\n    3,\n    false,\n    {\n        \"one\": 1\n    }\n]");
@@ -38,7 +38,7 @@ TEST_CASE("serialization")
         SECTION("given fill")
         {
             std::stringstream ss;
-            json j = {"foo", 1, 2, 3, false, {{"one", 1}}};
+            const json j = {"foo", 1, 2, 3, false, {{"one", 1}}};
             ss << std::setw(1) << std::setfill('\t') << j;
             CHECK(ss.str() ==
                   "[\n\t\"foo\",\n\t1,\n\t2,\n\t3,\n\tfalse,\n\t{\n\t\t\"one\": 1\n\t}\n]");
@@ -50,7 +50,7 @@ TEST_CASE("serialization")
         SECTION("no given width")
         {
             std::stringstream ss;
-            json j = {"foo", 1, 2, 3, false, {{"one", 1}}};
+            const json j = {"foo", 1, 2, 3, false, {{"one", 1}}};
             j >> ss;
             CHECK(ss.str() == "[\"foo\",1,2,3,false,{\"one\":1}]");
         }
@@ -58,7 +58,7 @@ TEST_CASE("serialization")
         SECTION("given width")
         {
             std::stringstream ss;
-            json j = {"foo", 1, 2, 3, false, {{"one", 1}}};
+            const json j = {"foo", 1, 2, 3, false, {{"one", 1}}};
             ss.width(4);
             j >> ss;
             CHECK(ss.str() ==
@@ -68,7 +68,7 @@ TEST_CASE("serialization")
         SECTION("given fill")
         {
             std::stringstream ss;
-            json j = {"foo", 1, 2, 3, false, {{"one", 1}}};
+            const json j = {"foo", 1, 2, 3, false, {{"one", 1}}};
             ss.width(1);
             ss.fill('\t');
             j >> ss;
@@ -81,7 +81,7 @@ TEST_CASE("serialization")
     {
         SECTION("invalid character")
         {
-            json j = "ä\xA9ü";
+            const json j = "ä\xA9ü";
 
             CHECK_THROWS_WITH_AS(j.dump(), "[json.exception.type_error.316] invalid UTF-8 byte at index 2: 0xA9", json::type_error&);
             CHECK_THROWS_WITH_AS(j.dump(1, ' ', false, json::error_handler_t::strict), "[json.exception.type_error.316] invalid UTF-8 byte at index 2: 0xA9", json::type_error&);
@@ -92,7 +92,7 @@ TEST_CASE("serialization")
 
         SECTION("ending with incomplete character")
         {
-            json j = "123\xC2";
+            const json j = "123\xC2";
 
             CHECK_THROWS_WITH_AS(j.dump(), "[json.exception.type_error.316] incomplete UTF-8 string; last byte: 0xC2", json::type_error&);
             CHECK_THROWS_AS(j.dump(1, ' ', false, json::error_handler_t::strict), json::type_error&);
@@ -103,7 +103,7 @@ TEST_CASE("serialization")
 
         SECTION("unexpected character")
         {
-            json j = "123\xF1\xB0\x34\x35\x36";
+            const json j = "123\xF1\xB0\x34\x35\x36";
 
             CHECK_THROWS_WITH_AS(j.dump(), "[json.exception.type_error.316] invalid UTF-8 byte at index 5: 0x34", json::type_error&);
             CHECK_THROWS_AS(j.dump(1, ' ', false, json::error_handler_t::strict), json::type_error&);
@@ -120,7 +120,7 @@ TEST_CASE("serialization")
 
             auto test = [&](std::string const & input, std::string const & expected)
             {
-                json j = input;
+                const json j = input;
                 CHECK(j.dump(-1, ' ', true, json::error_handler_t::replace) == "\"" + expected + "\"");
             };
 
@@ -154,7 +154,7 @@ TEST_CASE("serialization")
         auto test = [&](std::string const & input, std::string const & expected)
         {
             using std::to_string;
-            json j = input;
+            const json j = input;
             CHECK(to_string(j) == "\"" + expected + "\"");
         };
 
@@ -170,14 +170,14 @@ TEST_CASE_TEMPLATE("serialization for extreme integer values", T, int32_t, uint3
     SECTION("minimum")
     {
         constexpr auto minimum = (std::numeric_limits<T>::min)();
-        json j = minimum;
+        const json j = minimum;
         CHECK(j.dump() == std::to_string(minimum));
     }
 
     SECTION("maximum")
     {
         constexpr auto maximum = (std::numeric_limits<T>::max)();
-        json j = maximum;
+        const json j = maximum;
         CHECK(j.dump() == std::to_string(maximum));
     }
 }
@@ -189,15 +189,15 @@ TEST_CASE("dump with binary values")
     auto binary_with_subtype = json::binary({1, 2, 3, 4}, 128);
     auto binary_empty_with_subtype = json::binary({}, 128);
 
-    json object = {{"key", binary}};
-    json object_empty = {{"key", binary_empty}};
-    json object_with_subtype = {{"key", binary_with_subtype}};
-    json object_empty_with_subtype = {{"key", binary_empty_with_subtype}};
+    const json object = {{"key", binary}};
+    const json object_empty = {{"key", binary_empty}};
+    const json object_with_subtype = {{"key", binary_with_subtype}};
+    const json object_empty_with_subtype = {{"key", binary_empty_with_subtype}};
 
-    json array = {"value", 1, binary};
-    json array_empty = {"value", 1, binary_empty};
-    json array_with_subtype = {"value", 1, binary_with_subtype};
-    json array_empty_with_subtype = {"value", 1, binary_empty_with_subtype};
+    const json array = {"value", 1, binary};
+    const json array_empty = {"value", 1, binary_empty};
+    const json array_with_subtype = {"value", 1, binary_with_subtype};
+    const json array_empty_with_subtype = {"value", 1, binary_empty_with_subtype};
 
     SECTION("normal")
     {
diff --git a/tests/src/unit-testsuites.cpp b/tests/src/unit-testsuites.cpp
index 48cb07255..e0cc127b9 100644
--- a/tests/src/unit-testsuites.cpp
+++ b/tests/src/unit-testsuites.cpp
@@ -302,7 +302,7 @@ TEST_CASE("compliance tests from nativejson-benchmark")
                                      (std::istreambuf_iterator<char>()) );
 
             CAPTURE(json_string)
-            json j = json::parse(json_string);
+            const json j = json::parse(json_string);
             CHECK(j.dump() == json_string);
         }
     }
@@ -363,35 +363,35 @@ TEST_CASE("json.org examples")
     }
     SECTION("FILE 1.json")
     {
-        std::unique_ptr<std::FILE, decltype(&std::fclose)> f(std::fopen(TEST_DATA_DIRECTORY "/json.org/1.json", "r"), &std::fclose);
+        const std::unique_ptr<std::FILE, decltype(&std::fclose)> f(std::fopen(TEST_DATA_DIRECTORY "/json.org/1.json", "r"), &std::fclose);
         json _;
         CHECK_NOTHROW(_ = json::parse(f.get()));
     }
 
     SECTION("FILE 2.json")
     {
-        std::unique_ptr<std::FILE, decltype(&std::fclose)> f(std::fopen(TEST_DATA_DIRECTORY "/json.org/2.json", "r"), &std::fclose);
+        const std::unique_ptr<std::FILE, decltype(&std::fclose)> f(std::fopen(TEST_DATA_DIRECTORY "/json.org/2.json", "r"), &std::fclose);
         json _;
         CHECK_NOTHROW(_ = json::parse(f.get()));
     }
 
     SECTION("FILE 3.json")
     {
-        std::unique_ptr<std::FILE, decltype(&std::fclose)> f(std::fopen(TEST_DATA_DIRECTORY "/json.org/3.json", "r"), &std::fclose);
+        const std::unique_ptr<std::FILE, decltype(&std::fclose)> f(std::fopen(TEST_DATA_DIRECTORY "/json.org/3.json", "r"), &std::fclose);
         json _;
         CHECK_NOTHROW(_ = json::parse(f.get()));
     }
 
     SECTION("FILE 4.json")
     {
-        std::unique_ptr<std::FILE, decltype(&std::fclose)> f(std::fopen(TEST_DATA_DIRECTORY "/json.org/4.json", "r"), &std::fclose);
+        const std::unique_ptr<std::FILE, decltype(&std::fclose)> f(std::fopen(TEST_DATA_DIRECTORY "/json.org/4.json", "r"), &std::fclose);
         json _;
         CHECK_NOTHROW(_ = json::parse(f.get()));
     }
 
     SECTION("FILE 5.json")
     {
-        std::unique_ptr<std::FILE, decltype(&std::fclose)> f(std::fopen(TEST_DATA_DIRECTORY "/json.org/5.json", "r"), &std::fclose);
+        const std::unique_ptr<std::FILE, decltype(&std::fclose)> f(std::fopen(TEST_DATA_DIRECTORY "/json.org/5.json", "r"), &std::fclose);
         json _;
         CHECK_NOTHROW(_ = json::parse(f.get()));
     }
@@ -1340,12 +1340,12 @@ std::string trim(const std::string& str);
 // from https://stackoverflow.com/a/25829178/266378
 std::string trim(const std::string& str)
 {
-    size_t first = str.find_first_not_of(' ');
+    const size_t first = str.find_first_not_of(' ');
     if (std::string::npos == first)
     {
         return str;
     }
-    size_t last = str.find_last_not_of(' ');
+    const size_t last = str.find_last_not_of(' ');
     return str.substr(first, (last - first + 1));
 }
 } // namespace
@@ -1384,7 +1384,7 @@ TEST_CASE("Big List of Naughty Strings")
 
             // check roundtrip
             CAPTURE(line)
-            json j = json::parse(line);
+            const json j = json::parse(line);
             CHECK(j.dump() == line);
         }
     }
diff --git a/tests/src/unit-to_chars.cpp b/tests/src/unit-to_chars.cpp
index 0d5fcd422..d9f75ea2f 100644
--- a/tests/src/unit-to_chars.cpp
+++ b/tests/src/unit-to_chars.cpp
@@ -61,11 +61,11 @@ float make_float(uint64_t f, int e)
         e--;
     }
 
-    uint64_t biased_exponent = (e == kDenormalExponent && (f & kHiddenBit) == 0)
-                               ? 0
-                               : static_cast<uint64_t>(e + kExponentBias);
+    const uint64_t biased_exponent = (e == kDenormalExponent && (f & kHiddenBit) == 0)
+                                     ? 0
+                                     : static_cast<uint64_t>(e + kExponentBias);
 
-    uint64_t bits = (f & kSignificandMask) | (biased_exponent << kPhysicalSignificandSize);
+    const uint64_t bits = (f & kSignificandMask) | (biased_exponent << kPhysicalSignificandSize);
     return reinterpret_bits<float>(static_cast<uint32_t>(bits));
 }
 
@@ -113,11 +113,11 @@ double make_double(uint64_t f, int e)
         e--;
     }
 
-    uint64_t biased_exponent = (e == kDenormalExponent && (f & kHiddenBit) == 0)
-                               ? 0
-                               : static_cast<uint64_t>(e + kExponentBias);
+    const uint64_t biased_exponent = (e == kDenormalExponent && (f & kHiddenBit) == 0)
+                                     ? 0
+                                     : static_cast<uint64_t>(e + kExponentBias);
 
-    uint64_t bits = (f & kSignificandMask) | (biased_exponent << kPhysicalSignificandSize);
+    const uint64_t bits = (f & kSignificandMask) | (biased_exponent << kPhysicalSignificandSize);
     return reinterpret_bits<double>(bits);
 }
 } // namespace
@@ -458,7 +458,7 @@ TEST_CASE("formatting")
     {
         auto check_integer = [](std::int64_t number, const std::string & expected)
         {
-            nlohmann::json j = number;
+            const nlohmann::json j = number;
             CHECK(j.dump() == expected);
         };
 
diff --git a/tests/src/unit-unicode1.cpp b/tests/src/unit-unicode1.cpp
index 0b87cfa9d..f7a6ad197 100644
--- a/tests/src/unit-unicode1.cpp
+++ b/tests/src/unit-unicode1.cpp
@@ -233,9 +233,9 @@ void roundtrip(bool success_expected, const std::string& s)
     json _;
 
     // create JSON string value
-    json j = s;
+    const json j = s;
     // create JSON text
-    std::string ps = std::string("\"") + s + "\"";
+    const std::string ps = std::string("\"") + s + "\"";
 
     if (success_expected)
     {
@@ -253,7 +253,7 @@ void roundtrip(bool success_expected, const std::string& s)
         CHECK_NOTHROW(_ = json::parse(j.dump()));
 
         // after roundtrip, the same string is stored
-        json jr = json::parse(j.dump());
+        const json jr = json::parse(j.dump());
         CHECK(jr.get<std::string>() == s);
     }
     else
diff --git a/tests/src/unit-user_defined_input.cpp b/tests/src/unit-user_defined_input.cpp
index febc14c7c..576c81ea9 100644
--- a/tests/src/unit-user_defined_input.cpp
+++ b/tests/src/unit-user_defined_input.cpp
@@ -45,7 +45,7 @@ const char* end(const MyContainer& c)
 TEST_CASE("Custom container non-member begin/end")
 {
 
-    MyContainer data{"[1,2,3,4]"};
+    const MyContainer data{"[1,2,3,4]"};
     json as_json = json::parse(data);
     CHECK(as_json.at(0) == 1);
     CHECK(as_json.at(1) == 2);
@@ -71,7 +71,7 @@ TEST_CASE("Custom container member begin/end")
         }
     };
 
-    MyContainer2 data{"[1,2,3,4]"};
+    const MyContainer2 data{"[1,2,3,4]"};
     json as_json = json::parse(data);
     CHECK(as_json.at(0) == 1);
     CHECK(as_json.at(1) == 2);
@@ -117,8 +117,8 @@ TEST_CASE("Custom iterator")
     CHECK(std::is_same<MyIterator::reference, const char&>::value);
     CHECK(std::is_same<MyIterator::iterator_category, std::input_iterator_tag>::value);
 
-    MyIterator begin{raw_data};
-    MyIterator end{raw_data + strlen(raw_data)}; // NOLINT(cppcoreguidelines-pro-bounds-pointer-arithmetic)
+    const MyIterator begin{raw_data};
+    const MyIterator end{raw_data + strlen(raw_data)}; // NOLINT(cppcoreguidelines-pro-bounds-pointer-arithmetic)
 
     json as_json = json::parse(begin, end);
     CHECK(as_json.at(0) == 1);