diff --git a/test/src/unit-alt-string.cpp b/test/src/unit-alt-string.cpp
index b51a5a91d..b526ae20f 100644
--- a/test/src/unit-alt-string.cpp
+++ b/test/src/unit-alt-string.cpp
@@ -152,7 +152,7 @@ class alt_string
   private:
     std::string str_impl {};
 
-    friend bool ::operator<(const char*, const alt_string&);
+    friend bool ::operator<(const char* /*op1*/, const alt_string& /*op2*/);
 };
 
 void int_to_string(alt_string& target, std::size_t value)
@@ -233,24 +233,24 @@ TEST_CASE("alternative string type")
 
     SECTION("parse")
     {
-        auto doc = alt_json::parse("{\"foo\": \"bar\"}");
+        auto doc = alt_json::parse(R"({"foo": "bar"})");
         alt_string dump = doc.dump();
         CHECK(dump == R"({"foo":"bar"})");
     }
 
     SECTION("items")
     {
-        auto doc = alt_json::parse("{\"foo\": \"bar\"}");
+        auto doc = alt_json::parse(R"({"foo": "bar"})");
 
-        for ( auto item : doc.items() )
+        for (const auto& item : doc.items())
         {
-            CHECK( item.key() == "foo" );
-            CHECK( item.value() == "bar" );
+            CHECK(item.key() == "foo");
+            CHECK(item.value() == "bar");
         }
 
-        auto doc_array = alt_json::parse("[\"foo\", \"bar\"]");
+        auto doc_array = alt_json::parse(R"(["foo", "bar"])");
 
-        for ( auto item : doc_array.items() )
+        for (const auto& item : doc_array.items())
         {
             if (item.key() == "0" )
             {
@@ -258,11 +258,11 @@ TEST_CASE("alternative string type")
             }
             else if (item.key() == "1" )
             {
-                CHECK( item.value() == "bar" );
+                CHECK(item.value() == "bar");
             }
             else
             {
-                CHECK( false );
+                CHECK(false);
             }
         }
     }
diff --git a/test/src/unit-bson.cpp b/test/src/unit-bson.cpp
index 3be72c7d4..e0e020de0 100644
--- a/test/src/unit-bson.cpp
+++ b/test/src/unit-bson.cpp
@@ -683,42 +683,42 @@ class SaxCountdown
         return events_left-- > 0;
     }
 
-    bool boolean(bool)
+    bool boolean(bool /*unused*/)
     {
         return events_left-- > 0;
     }
 
-    bool number_integer(json::number_integer_t)
+    bool number_integer(json::number_integer_t /*unused*/)
     {
         return events_left-- > 0;
     }
 
-    bool number_unsigned(json::number_unsigned_t)
+    bool number_unsigned(json::number_unsigned_t /*unused*/)
     {
         return events_left-- > 0;
     }
 
-    bool number_float(json::number_float_t, const std::string&)
+    bool number_float(json::number_float_t /*unused*/, const std::string& /*unused*/)
     {
         return events_left-- > 0;
     }
 
-    bool string(std::string&)
+    bool string(std::string& /*unused*/)
     {
         return events_left-- > 0;
     }
 
-    bool binary(std::vector<std::uint8_t>&)
+    bool binary(std::vector<std::uint8_t>& /*unused*/)
     {
         return events_left-- > 0;
     }
 
-    bool start_object(std::size_t)
+    bool start_object(std::size_t /*unused*/)
     {
         return events_left-- > 0;
     }
 
-    bool key(std::string&)
+    bool key(std::string& /*unused*/)
     {
         return events_left-- > 0;
     }
@@ -728,7 +728,7 @@ class SaxCountdown
         return events_left-- > 0;
     }
 
-    bool start_array(std::size_t)
+    bool start_array(std::size_t /*unused*/)
     {
         return events_left-- > 0;
     }
@@ -738,7 +738,7 @@ class SaxCountdown
         return events_left-- > 0;
     }
 
-    bool parse_error(std::size_t, const std::string&, const json::exception&)
+    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/, const json::exception& /*unused*/)
     {
         return false;
     }
@@ -746,7 +746,7 @@ class SaxCountdown
   private:
     int events_left = 0;
 };
-}
+} // namespace
 
 TEST_CASE("Incomplete BSON Input")
 {
diff --git a/test/src/unit-comparison.cpp b/test/src/unit-comparison.cpp
index e375feca4..56b38cf6b 100644
--- a/test/src/unit-comparison.cpp
+++ b/test/src/unit-comparison.cpp
@@ -41,7 +41,7 @@ bool f(A a, B b, U u = U())
 {
     return u(a, b);
 }
-}
+} // namespace
 
 TEST_CASE("lexicographical comparison operators")
 {
@@ -143,10 +143,10 @@ TEST_CASE("lexicographical comparison operators")
 
             // comparison with discarded elements
             json j_discarded(json::value_t::discarded);
-            for (size_t i = 0; i < j_values.size(); ++i)
+            for (const auto& v : j_values)
             {
-                CHECK( (j_values[i] == j_discarded) == false);
-                CHECK( (j_discarded == j_values[i]) == false);
+                CHECK( (v == j_discarded) == false);
+                CHECK( (j_discarded == v) == false);
                 CHECK( (j_discarded == j_discarded) == false);
             }
 
diff --git a/test/src/unit-constructor2.cpp b/test/src/unit-constructor2.cpp
index 27f4dfdcb..a32ad2eef 100644
--- a/test/src/unit-constructor2.cpp
+++ b/test/src/unit-constructor2.cpp
@@ -188,19 +188,19 @@ TEST_CASE("other constructors and destructor")
     {
         SECTION("object")
         {
-            auto j = new json {{"foo", 1}, {"bar", false}};
+            auto* j = new json {{"foo", 1}, {"bar", false}};
             delete j;
         }
 
         SECTION("array")
         {
-            auto j = new json {"foo", 1, 1u, false, 23.42};
+            auto* j = new json {"foo", 1, 1u, false, 23.42};
             delete j;
         }
 
         SECTION("string")
         {
-            auto j = new json("Hello world");
+            auto* j = new json("Hello world");
             delete j;
         }
     }
diff --git a/test/src/unit-convenience.cpp b/test/src/unit-convenience.cpp
index c75edac4e..1d98cd8be 100644
--- a/test/src/unit-convenience.cpp
+++ b/test/src/unit-convenience.cpp
@@ -37,7 +37,7 @@ using nlohmann::json;
 
 namespace
 {
-void check_escaped(const char* original, const char* escaped = "", const bool ensure_ascii = false);
+void check_escaped(const char* original, const char* escaped = "", bool ensure_ascii = false);
 void check_escaped(const char* original, const char* escaped, const bool ensure_ascii)
 {
     std::stringstream ss;
@@ -45,7 +45,7 @@ void check_escaped(const char* original, const char* escaped, const bool ensure_
     s.dump_escaped(original, ensure_ascii);
     CHECK(ss.str() == escaped);
 }
-}
+} // namespace
 
 TEST_CASE("convenience functions")
 {
diff --git a/test/src/unit-json_patch.cpp b/test/src/unit-json_patch.cpp
index 2ad7aadb8..a5deef548 100644
--- a/test/src/unit-json_patch.cpp
+++ b/test/src/unit-json_patch.cpp
@@ -1258,7 +1258,7 @@ TEST_CASE("JSON patch")
 
     SECTION("Tests from github.com/json-patch/json-patch-tests")
     {
-        for (auto filename :
+        for (const auto* filename :
                 {
                     TEST_DATA_DIRECTORY "/json-patch-tests/spec_tests.json",
                     TEST_DATA_DIRECTORY "/json-patch-tests/tests.json"
diff --git a/test/src/unit-json_pointer.cpp b/test/src/unit-json_pointer.cpp
index 14d8cd183..9894cef45 100644
--- a/test/src/unit-json_pointer.cpp
+++ b/test/src/unit-json_pointer.cpp
@@ -527,7 +527,7 @@ TEST_CASE("JSON pointers")
 
     SECTION("string representation")
     {
-        for (auto ptr :
+        for (const auto* ptr :
                 {"", "/foo", "/foo/0", "/", "/a~1b", "/c%d", "/e^f", "/g|h", "/i\\j", "/k\"l", "/ ", "/m~0n"
                 })
         {
diff --git a/test/src/unit-msgpack.cpp b/test/src/unit-msgpack.cpp
index e49a4203c..d3c60cf9a 100644
--- a/test/src/unit-msgpack.cpp
+++ b/test/src/unit-msgpack.cpp
@@ -52,42 +52,42 @@ class SaxCountdown
         return events_left-- > 0;
     }
 
-    bool boolean(bool)
+    bool boolean(bool /*unused*/)
     {
         return events_left-- > 0;
     }
 
-    bool number_integer(json::number_integer_t)
+    bool number_integer(json::number_integer_t /*unused*/)
     {
         return events_left-- > 0;
     }
 
-    bool number_unsigned(json::number_unsigned_t)
+    bool number_unsigned(json::number_unsigned_t /*unused*/)
     {
         return events_left-- > 0;
     }
 
-    bool number_float(json::number_float_t, const std::string&)
+    bool number_float(json::number_float_t /*unused*/, const std::string& /*unused*/)
     {
         return events_left-- > 0;
     }
 
-    bool string(std::string&)
+    bool string(std::string& /*unused*/)
     {
         return events_left-- > 0;
     }
 
-    bool binary(std::vector<std::uint8_t>&)
+    bool binary(std::vector<std::uint8_t>& /*unused*/)
     {
         return events_left-- > 0;
     }
 
-    bool start_object(std::size_t)
+    bool start_object(std::size_t /*unused*/)
     {
         return events_left-- > 0;
     }
 
-    bool key(std::string&)
+    bool key(std::string& /*unused*/)
     {
         return events_left-- > 0;
     }
@@ -97,7 +97,7 @@ class SaxCountdown
         return events_left-- > 0;
     }
 
-    bool start_array(std::size_t)
+    bool start_array(std::size_t /*unused*/)
     {
         return events_left-- > 0;
     }
@@ -107,7 +107,7 @@ class SaxCountdown
         return events_left-- > 0;
     }
 
-    bool parse_error(std::size_t, const std::string&, const json::exception&)
+    bool parse_error(std::size_t /*unused*/, const std::string& /*unused*/, const json::exception& /*unused*/)
     {
         return false;
     }
@@ -258,7 +258,7 @@ TEST_CASE("MessagePack")
 
                         // check individual bytes
                         CHECK(result[0] == 0xcc);
-                        uint8_t restored = static_cast<uint8_t>(result[1]);
+                        auto restored = static_cast<uint8_t>(result[1]);
                         CHECK(restored == i);
 
                         // roundtrip
@@ -293,7 +293,7 @@ TEST_CASE("MessagePack")
 
                         // check individual bytes
                         CHECK(result[0] == 0xcd);
-                        uint16_t restored = static_cast<uint16_t>(static_cast<uint8_t>(result[1]) * 256 + static_cast<uint8_t>(result[2]));
+                        auto restored = static_cast<uint16_t>(static_cast<uint8_t>(result[1]) * 256 + static_cast<uint8_t>(result[2]));
                         CHECK(restored == i);
 
                         // roundtrip
@@ -436,7 +436,7 @@ TEST_CASE("MessagePack")
                     const auto result = json::to_msgpack(j);
                     CHECK(result == expected);
 
-                    int16_t restored = static_cast<int16_t>((result[1] << 8) + result[2]);
+                    auto restored = static_cast<int16_t>((result[1] << 8) + result[2]);
                     CHECK(restored == -9263);
 
                     // roundtrip
@@ -469,7 +469,7 @@ TEST_CASE("MessagePack")
 
                         // check individual bytes
                         CHECK(result[0] == 0xd1);
-                        int16_t restored = static_cast<int16_t>((result[1] << 8) + result[2]);
+                        auto restored = static_cast<int16_t>((result[1] << 8) + result[2]);
                         CHECK(restored == i);
 
                         // roundtrip
@@ -630,7 +630,7 @@ TEST_CASE("MessagePack")
 
                         // check individual bytes
                         CHECK(result[0] == 0xcc);
-                        uint8_t restored = static_cast<uint8_t>(result[1]);
+                        auto restored = static_cast<uint8_t>(result[1]);
                         CHECK(restored == i);
 
                         // roundtrip
@@ -664,7 +664,7 @@ TEST_CASE("MessagePack")
 
                         // check individual bytes
                         CHECK(result[0] == 0xcd);
-                        uint16_t restored = static_cast<uint16_t>(static_cast<uint8_t>(result[1]) * 256 + static_cast<uint8_t>(result[2]));
+                        auto restored = static_cast<uint16_t>(static_cast<uint8_t>(result[1]) * 256 + static_cast<uint8_t>(result[2]));
                         CHECK(restored == i);
 
                         // roundtrip
@@ -1088,7 +1088,7 @@ TEST_CASE("MessagePack")
 
             SECTION("{\"a\": {\"b\": {\"c\": {}}}}")
             {
-                json j = json::parse("{\"a\": {\"b\": {\"c\": {}}}}");
+                json j = json::parse(R"({"a": {"b": {"c": {}}}})");
                 std::vector<uint8_t> expected =
                 {
                     0x81, 0xa1, 0x61, 0x81, 0xa1, 0x62, 0x81, 0xa1, 0x63, 0x80
@@ -1870,7 +1870,7 @@ TEST_CASE("MessagePack roundtrips" * doctest::skip())
                 // parse MessagePack file
                 auto packed = utils::read_binary_file(filename + ".msgpack");
 
-                if (!exclude_packed.count(filename))
+                if (exclude_packed.count(filename) == 0u)
                 {
                     {
                         INFO_WITH_TEMP(filename + ": output adapters: std::vector<uint8_t>");
diff --git a/test/src/unit-ordered_map.cpp b/test/src/unit-ordered_map.cpp
index 645183d8c..47d049de6 100644
--- a/test/src/unit-ordered_map.cpp
+++ b/test/src/unit-ordered_map.cpp
@@ -49,6 +49,7 @@ TEST_CASE("ordered_map")
             std::map<std::string, std::string> m {{"eins", "one"}, {"zwei", "two"}, {"drei", "three"}};
             ordered_map<std::string, std::string> om(m.begin(), m.end());
             const auto com = om;
+            om.clear(); // silence a warning by forbidding having "const auto& com = om;"
             CHECK(com.size() == 3);
         }
     }
diff --git a/test/src/unit-readme.cpp b/test/src/unit-readme.cpp
index ed2a4dcee..3bf733948 100644
--- a/test/src/unit-readme.cpp
+++ b/test/src/unit-readme.cpp
@@ -52,7 +52,7 @@ TEST_CASE("README" * doctest::skip())
 {
     {
         // redirect std::cout for the README file
-        auto old_cout_buffer = std::cout.rdbuf();
+        auto* old_cout_buffer = std::cout.rdbuf();
         std::ostringstream new_stream;
         std::cout.rdbuf(new_stream.rdbuf());
         {
diff --git a/test/src/unit-reference_access.cpp b/test/src/unit-reference_access.cpp
index c98367765..125c7ea4f 100644
--- a/test/src/unit-reference_access.cpp
+++ b/test/src/unit-reference_access.cpp
@@ -56,11 +56,11 @@ TEST_CASE("reference access")
         json value = {{"one", 1}, {"two", 2}};
 
         // check if references are returned correctly
-        test_type& p1 = value.get_ref<test_type&>();
+        auto& p1 = value.get_ref<test_type&>();
         CHECK(&p1 == value.get_ptr<test_type*>());
         CHECK(p1 == value.get<test_type>());
 
-        const test_type& p2 = value.get_ref<const test_type&>();
+        const auto& p2 = value.get_ref<const test_type&>();
         CHECK(&p2 == value.get_ptr<const test_type*>());
         CHECK(p2 == value.get<test_type>());
 
@@ -95,7 +95,7 @@ TEST_CASE("reference access")
         // test_type& p1 = value.get_ref<test_type&>();
 
         // check if references are returned correctly
-        const test_type& p2 = value.get_ref<const test_type&>();
+        const auto& p2 = value.get_ref<const test_type&>();
         CHECK(&p2 == value.get_ptr<const test_type*>());
         CHECK(p2 == value.get<test_type>());
     }
@@ -106,11 +106,11 @@ TEST_CASE("reference access")
         json value = {1, 2, 3, 4};
 
         // check if references are returned correctly
-        test_type& p1 = value.get_ref<test_type&>();
+        auto& p1 = value.get_ref<test_type&>();
         CHECK(&p1 == value.get_ptr<test_type*>());
         CHECK(p1 == value.get<test_type>());
 
-        const test_type& p2 = value.get_ref<const test_type&>();
+        const auto& p2 = value.get_ref<const test_type&>();
         CHECK(&p2 == value.get_ptr<const test_type*>());
         CHECK(p2 == value.get<test_type>());
 
@@ -142,11 +142,11 @@ TEST_CASE("reference access")
         json value = "hello";
 
         // check if references are returned correctly
-        test_type& p1 = value.get_ref<test_type&>();
+        auto& p1 = value.get_ref<test_type&>();
         CHECK(&p1 == value.get_ptr<test_type*>());
         CHECK(p1 == value.get<test_type>());
 
-        const test_type& p2 = value.get_ref<const test_type&>();
+        const auto& p2 = value.get_ref<const test_type&>();
         CHECK(&p2 == value.get_ptr<const test_type*>());
         CHECK(p2 == value.get<test_type>());
 
@@ -178,11 +178,11 @@ TEST_CASE("reference access")
         json value = false;
 
         // check if references are returned correctly
-        test_type& p1 = value.get_ref<test_type&>();
+        auto& p1 = value.get_ref<test_type&>();
         CHECK(&p1 == value.get_ptr<test_type*>());
         CHECK(p1 == value.get<test_type>());
 
-        const test_type& p2 = value.get_ref<const test_type&>();
+        const auto& p2 = value.get_ref<const test_type&>();
         CHECK(&p2 == value.get_ptr<const test_type*>());
         CHECK(p2 == value.get<test_type>());
 
@@ -214,11 +214,11 @@ TEST_CASE("reference access")
         json value = -23;
 
         // check if references are returned correctly
-        test_type& p1 = value.get_ref<test_type&>();
+        auto& p1 = value.get_ref<test_type&>();
         CHECK(&p1 == value.get_ptr<test_type*>());
         CHECK(p1 == value.get<test_type>());
 
-        const test_type& p2 = value.get_ref<const test_type&>();
+        const auto& p2 = value.get_ref<const test_type&>();
         CHECK(&p2 == value.get_ptr<const test_type*>());
         CHECK(p2 == value.get<test_type>());
 
@@ -250,11 +250,11 @@ TEST_CASE("reference access")
         json value = 23u;
 
         // check if references are returned correctly
-        test_type& p1 = value.get_ref<test_type&>();
+        auto& p1 = value.get_ref<test_type&>();
         CHECK(&p1 == value.get_ptr<test_type*>());
         CHECK(p1 == value.get<test_type>());
 
-        const test_type& p2 = value.get_ref<const test_type&>();
+        const auto& p2 = value.get_ref<const test_type&>();
         CHECK(&p2 == value.get_ptr<const test_type*>());
         CHECK(p2 == value.get<test_type>());
 
@@ -286,11 +286,11 @@ TEST_CASE("reference access")
         json value = 42.23;
 
         // check if references are returned correctly
-        test_type& p1 = value.get_ref<test_type&>();
+        auto& p1 = value.get_ref<test_type&>();
         CHECK(&p1 == value.get_ptr<test_type*>());
         CHECK(p1 == value.get<test_type>());
 
-        const test_type& p2 = value.get_ref<const test_type&>();
+        const auto& p2 = value.get_ref<const test_type&>();
         CHECK(&p2 == value.get_ptr<const test_type*>());
         CHECK(p2 == value.get<test_type>());
 
diff --git a/test/src/unit-regression2.cpp b/test/src/unit-regression2.cpp
index 107d16b8c..5ea8de63d 100644
--- a/test/src/unit-regression2.cpp
+++ b/test/src/unit-regression2.cpp
@@ -122,7 +122,7 @@ struct adl_serializer<NonDefaultFromJsonStruct>
         return {};
     }
 };
-}
+} // namespace nlohmann
 
 /////////////////////////////////////////////////////////////////////
 // for #1805
@@ -139,7 +139,7 @@ TEST_CASE("regression tests 2")
 {
     SECTION("issue #1001 - Fix memory leak during parser callback")
     {
-        auto geojsonExample = R"(
+        const auto* geojsonExample = R"(
           { "type": "FeatureCollection",
             "features": [
               { "type": "Feature",
@@ -174,7 +174,7 @@ TEST_CASE("regression tests 2")
                ]
              })";
 
-        json::parser_callback_t cb = [&](int, json::parse_event_t event, json & parsed)
+        json::parser_callback_t cb = [&](int /*level*/, json::parse_event_t event, json & parsed)
         {
             // skip uninteresting events
             if (event == json::parse_event_t::value && !parsed.is_primitive())
@@ -290,7 +290,7 @@ TEST_CASE("regression tests 2")
             json dump_test;
             dump_test["1"] = std::string(length, -1);
 
-            std::string expected = "{\"1\":\"";
+            std::string expected = R"({"1":")";
             for (int i = 0; i < length; ++i)
             {
                 expected += "\\ufffd";
@@ -307,7 +307,7 @@ TEST_CASE("regression tests 2")
             json dump_test;
             dump_test["1"] = std::string(length, -2);
 
-            std::string expected = "{\"1\":\"";
+            std::string expected = R"({"1":")";
             for (int i = 0; i < length; ++i)
             {
                 expected += "\xEF\xBF\xBD";
@@ -340,9 +340,9 @@ TEST_CASE("regression tests 2")
                 -54,  -28,  -26
             };
             std::string s;
-            for (unsigned i = 0; i < sizeof(data) / sizeof(int); i++)
+            for (int i : data)
             {
-                s += static_cast<char>(data[i]);
+                s += static_cast<char>(i);
             }
             dump_test["1"] = s;
             dump_test.dump(-1, ' ', true, nlohmann::json::error_handler_t::replace);
diff --git a/test/src/unit-to_chars.cpp b/test/src/unit-to_chars.cpp
index 2861928f8..b94b08755 100644
--- a/test/src/unit-to_chars.cpp
+++ b/test/src/unit-to_chars.cpp
@@ -38,7 +38,7 @@ using nlohmann::detail::dtoa_impl::reinterpret_bits;
 
 namespace
 {
-static float make_float(uint32_t sign_bit, uint32_t biased_exponent, uint32_t significand)
+float make_float(uint32_t sign_bit, uint32_t biased_exponent, uint32_t significand)
 {
     assert(sign_bit == 0 || sign_bit == 1);
     assert(biased_exponent <= 0xFF);
diff --git a/test/src/unit-udt.cpp b/test/src/unit-udt.cpp
index b333d0b65..be7827df3 100644
--- a/test/src/unit-udt.cpp
+++ b/test/src/unit-udt.cpp
@@ -34,8 +34,10 @@ using nlohmann::json;
 
 #include <array>
 #include <map>
+#include <memory>
 #include <string>
 #include <memory>
+#include <utility>
 
 namespace udt
 {
@@ -55,40 +57,40 @@ struct age
 struct name
 {
     std::string m_val;
-    name(const std::string rhs = "") : m_val(rhs) {}
+    name(std::string rhs = "") : m_val(std::move(rhs)) {}
 };
 
 struct address
 {
     std::string m_val;
-    address(const std::string rhs = "") : m_val(rhs) {}
+    address(std::string rhs = "") : m_val(std::move(rhs)) {}
 };
 
 struct person
 {
     age m_age;
     name m_name;
-    country m_country;
-    person() : m_age(), m_name(), m_country() {}
-    person(const age& a, const name& n, const country& c) : m_age(a), m_name(n), m_country(c) {}
+    country m_country{};
+    person() = default;
+    person(const age& a, name  n, const country& c) : m_age(a), m_name(std::move(n)), m_country(c) {}
 };
 
 struct contact
 {
     person m_person;
     address m_address;
-    contact() : m_person(), m_address() {}
-    contact(const person& p, const address& a) : m_person(p), m_address(a) {}
+    contact() = default;
+    contact(person p, address a) : m_person(std::move(p)), m_address(std::move(a)) {}
 };
 
 struct contact_book
 {
     name m_book_name;
     std::vector<contact> m_contacts;
-    contact_book() : m_book_name(), m_contacts() {}
-    contact_book(const name& n, const std::vector<contact>& c) : m_book_name(n), m_contacts(c) {}
+    contact_book() = default;
+    contact_book(name n, std::vector<contact> c) : m_book_name(std::move(n)), m_contacts(std::move(c)) {}
 };
-}
+} // namespace udt
 
 // to_json methods
 namespace udt
@@ -178,7 +180,7 @@ static bool operator==(const contact_book& lhs, const contact_book& rhs)
     return std::tie(lhs.m_book_name, lhs.m_contacts) ==
            std::tie(rhs.m_book_name, rhs.m_contacts);
 }
-}
+} // namespace udt
 
 // from_json methods
 namespace udt
@@ -207,7 +209,7 @@ static void from_json(const BasicJsonType& j, country& c)
     };
 
     const auto it = m.find(str);
-    // TODO test exceptions
+    // TODO(nlohmann) test exceptions
     c = it->second;
 }
 
@@ -235,7 +237,7 @@ static void from_json(const nlohmann::json& j, contact_book& cb)
     cb.m_book_name = j["name"].get<name>();
     cb.m_contacts = j["contacts"].get<std::vector<contact>>();
 }
-}
+} // namespace udt
 
 TEST_CASE("basic usage" * doctest::test_suite("udt"))
 {
@@ -345,10 +347,10 @@ namespace udt
 struct legacy_type
 {
     std::string number;
-    legacy_type() : number() {}
-    legacy_type(const std::string& n) : number(n) {}
+    legacy_type() = default;
+    legacy_type(std::string  n) : number(std::move(n)) {}
 };
-}
+} // namespace udt
 
 namespace nlohmann
 {
@@ -393,7 +395,7 @@ struct adl_serializer<udt::legacy_type>
         l.number = std::to_string(j.get<int>());
     }
 };
-}
+} // namespace nlohmann
 
 TEST_CASE("adl_serializer specialization" * doctest::test_suite("udt"))
 {
@@ -453,23 +455,23 @@ template <>
 struct adl_serializer<std::vector<float>>
 {
     using type = std::vector<float>;
-    static void to_json(json& j, const type&)
+    static void to_json(json& j, const type& /*type*/)
     {
         j = "hijacked!";
     }
 
-    static void from_json(const json&, type& opt)
+    static void from_json(const json& /*unnamed*/, type& opt)
     {
         opt = {42.0, 42.0, 42.0};
     }
 
     // preferred version
-    static type from_json(const json&)
+    static type from_json(const json& /*unnamed*/)
     {
         return {4.0, 5.0, 6.0};
     }
 };
-}
+} // namespace nlohmann
 
 TEST_CASE("even supported types can be specialized" * doctest::test_suite("udt"))
 {
@@ -504,13 +506,11 @@ struct adl_serializer<std::unique_ptr<T>>
         {
             return nullptr;
         }
-        else
-        {
-            return std::unique_ptr<T>(new T(j.get<T>()));
-        }
+
+        return std::unique_ptr<T>(new T(j.get<T>()));
     }
 };
-}
+} // namespace nlohmann
 
 TEST_CASE("Non-copyable types" * doctest::test_suite("udt"))
 {
@@ -566,8 +566,8 @@ struct pod_serializer
                    std::is_pod<U>::value && std::is_class<U>::value, int >::type = 0 >
     static void from_json(const  BasicJsonType& j, U& t)
     {
-        std::uint64_t value;
-        // TODO The following block is no longer relevant in this serializer, make another one that shows the issue
+        std::uint64_t value = 0;
+        // The following block is no longer relevant in this serializer, make another one that shows the issue
         // the problem arises only when one from_json method is defined without any constraint
         //
         // Why cannot we simply use: j.get<std::uint64_t>() ?
@@ -582,7 +582,7 @@ struct pod_serializer
         // calling get calls from_json, for now, we cannot do this in custom
         // serializers
         nlohmann::from_json(j, value);
-        auto bytes = static_cast<char*>(static_cast<void*>(&value));
+        auto* bytes = static_cast<char*>(static_cast<void*>(&value));
         std::memcpy(&t, bytes, sizeof(value));
     }
 
@@ -601,8 +601,8 @@ struct pod_serializer
                    std::is_pod<U>::value && std::is_class<U>::value, int >::type = 0 >
     static void to_json(BasicJsonType& j, const  T& t) noexcept
     {
-        auto bytes = static_cast< const unsigned char*>(static_cast<const void*>(&t));
-        std::uint64_t value;
+        const auto* bytes = static_cast< const unsigned char*>(static_cast<const void*>(&t));
+        std::uint64_t value = 0;
         std::memcpy(&value, bytes, sizeof(value));
         nlohmann::to_json(j, value);
     }
@@ -620,8 +620,8 @@ struct small_pod
 struct non_pod
 {
     std::string s;
-    non_pod() : s() {}
-    non_pod(const std::string& S) : s(S) {}
+    non_pod() = default;
+    non_pod(std::string S) : s(std::move(S)) {}
 };
 
 template <typename BasicJsonType>
@@ -651,7 +651,7 @@ static std::ostream& operator<<(std::ostream& os, small_pod l)
 {
     return os << "begin: " << l.begin << ", middle: " << l.middle << ", end: " << l.end;
 }
-}
+} // namespace udt
 
 TEST_CASE("custom serializer for pods" * doctest::test_suite("udt"))
 {
@@ -803,7 +803,7 @@ struct is_constructible_patched : std::false_type {};
 
 template <typename T>
 struct is_constructible_patched<T, decltype(void(json(std::declval<T>())))> : std::true_type {};
-}
+} // namespace
 
 TEST_CASE("an incomplete type does not trigger a compiler error in non-evaluated context" * doctest::test_suite("udt"))
 {
@@ -822,8 +822,8 @@ class Evil
     int m_i = 0;
 };
 
-void from_json(const json&, Evil&) {}
-}
+void from_json(const json& /*unused*/, Evil& /*unused*/) {}
+} // namespace
 
 TEST_CASE("Issue #924")
 {
diff --git a/test/src/unit-udt_macro.cpp b/test/src/unit-udt_macro.cpp
index a13ac006b..334305571 100644
--- a/test/src/unit-udt_macro.cpp
+++ b/test/src/unit-udt_macro.cpp
@@ -39,7 +39,7 @@ namespace persons
 class person_with_private_data
 {
   private:
-    std::string name = "";
+    std::string name;
     int age = 0;
     json metadata = nullptr;
 
@@ -62,7 +62,7 @@ class person_with_private_data
 class person_without_private_data_1
 {
   public:
-    std::string name = "";
+    std::string name;
     int age = 0;
     json metadata = nullptr;
 
@@ -84,7 +84,7 @@ class person_without_private_data_1
 class person_without_private_data_2
 {
   public:
-    std::string name = "";
+    std::string name;
     int age = 0;
     json metadata = nullptr;
 
diff --git a/test/src/unit-unicode.cpp b/test/src/unit-unicode.cpp
index acaca2888..0ffcb76dd 100644
--- a/test/src/unit-unicode.cpp
+++ b/test/src/unit-unicode.cpp
@@ -168,7 +168,7 @@ void check_utf8string(bool success_expected, int byte1, int byte2 = -1, int byte
         CHECK_THROWS_AS(_ = json::parse(json_string), json::parse_error&);
     }
 }
-}
+} // namespace
 
 TEST_CASE("Unicode" * doctest::skip())
 {
@@ -1159,7 +1159,7 @@ TEST_CASE("Unicode" * doctest::skip())
 
         SECTION("check JSON Pointers")
         {
-            for (auto s : j)
+            for (const auto& s : j)
             {
                 // skip non-string JSON values
                 if (!s.is_string())
@@ -1176,7 +1176,7 @@ TEST_CASE("Unicode" * doctest::skip())
                 }
 
                 // JSON Pointers must begin with "/"
-                ptr = "/" + ptr;
+                ptr.insert(0, "/");
 
                 CHECK_NOTHROW(json::json_pointer("/" + ptr));
 
@@ -1256,7 +1256,7 @@ void roundtrip(bool success_expected, const std::string& s)
         CHECK_THROWS_AS(_ = json::parse(ps), json::parse_error&);
     }
 }
-}
+} // namespace
 
 TEST_CASE("Markus Kuhn's UTF-8 decoder capability and stress test")
 {
diff --git a/test/src/unit-wstring.cpp b/test/src/unit-wstring.cpp
index a5b80be74..b8ee2eaeb 100644
--- a/test/src/unit-wstring.cpp
+++ b/test/src/unit-wstring.cpp
@@ -51,7 +51,7 @@ bool u32string_is_utf32()
 {
     return (std::u32string(U"💩") == std::u32string(U"\U0001F4A9"));
 }
-}
+} // namespace
 
 TEST_CASE("wide strings")
 {