Add unit tests for dump_integer

Add some unit tests for formatting integers
to keep code coverage as before.

test/src/unit-to_chars.cpp

@@ -471,4 +471,64 @@ TEST_CASE("formatting")
         check_double(  1.2345e+21,   "1.2344999999999999e+21" ); //  1.2345e+21                1.2344999999999999e+21    1.2345e21
         check_double(  1.2345e+22,   "1.2345e+22"             ); //  1.2345e+22                1.2345e+22                1.2345e22
     }
+
+    SECTION("integer")
+    {
+        auto check_integer = [](std::int64_t number, const std::string & expected)
+        {
+            nlohmann::json j = number;
+            CHECK(j.dump() == expected);
+        };
+
+        // edge cases
+        check_integer(INT64_MIN, "-9223372036854775808");
+        check_integer(INT64_MAX, "9223372036854775807");
+
+        // few random big integers
+        check_integer(-3456789012345678901LL, "-3456789012345678901");
+        check_integer(3456789012345678901LL, "3456789012345678901");
+        check_integer(-5678901234567890123LL, "-5678901234567890123");
+        check_integer(5678901234567890123LL, "5678901234567890123");
+
+        // integers with various digit counts
+        check_integer(-1000000000000000000LL, "-1000000000000000000");
+        check_integer(-100000000000000000LL, "-100000000000000000");
+        check_integer(-10000000000000000LL, "-10000000000000000");
+        check_integer(-1000000000000000LL, "-1000000000000000");
+        check_integer(-100000000000000LL, "-100000000000000");
+        check_integer(-10000000000000LL, "-10000000000000");
+        check_integer(-1000000000000LL, "-1000000000000");
+        check_integer(-100000000000LL, "-100000000000");
+        check_integer(-10000000000LL, "-10000000000");
+        check_integer(-1000000000LL, "-1000000000");
+        check_integer(-100000000LL, "-100000000");
+        check_integer(-10000000LL, "-10000000");
+        check_integer(-1000000LL, "-1000000");
+        check_integer(-100000LL, "-100000");
+        check_integer(-10000LL, "-10000");
+        check_integer(-1000LL, "-1000");
+        check_integer(-100LL, "-100");
+        check_integer(-10LL, "-10");
+        check_integer(-1LL, "-1");
+        check_integer(0, "0");
+        check_integer(1LL, "1");
+        check_integer(10LL, "10");
+        check_integer(100LL, "100");
+        check_integer(1000LL, "1000");
+        check_integer(10000LL, "10000");
+        check_integer(100000LL, "100000");
+        check_integer(1000000LL, "1000000");
+        check_integer(10000000LL, "10000000");
+        check_integer(100000000LL, "100000000");
+        check_integer(1000000000LL, "1000000000");
+        check_integer(10000000000LL, "10000000000");
+        check_integer(100000000000LL, "100000000000");
+        check_integer(1000000000000LL, "1000000000000");
+        check_integer(10000000000000LL, "10000000000000");
+        check_integer(100000000000000LL, "100000000000000");
+        check_integer(1000000000000000LL, "1000000000000000");
+        check_integer(10000000000000000LL, "10000000000000000");
+        check_integer(100000000000000000LL, "100000000000000000");
+        check_integer(1000000000000000000LL, "1000000000000000000");
+    }
 }