Add tests for all supported char types

tests/BUILD.bazel

@@ -97,6 +97,15 @@ cc_test(
     ],
 )
 
+cc_test(
+    name = "supported_chars_test",
+    srcs = ["supported_chars_test.cpp"],
+    deps = [
+        "//:fast_float",
+        "@doctest//doctest",
+    ],
+)
+
 cc_test(
     name = "string_test",
     srcs = ["string_test.cpp"],

tests/CMakeLists.txt

@@ -68,6 +68,7 @@ endfunction(fast_float_add_cpp_test)
 
 fast_float_add_cpp_test(rcppfastfloat_test)
 fast_float_add_cpp_test(wide_char_test)
+fast_float_add_cpp_test(supported_chars_test)
 fast_float_add_cpp_test(example_test)
 fast_float_add_cpp_test(example_comma_test)
 fast_float_add_cpp_test(basictest)

tests/supported_chars_test.cpp

@@ -0,0 +1,53 @@
+#include "fast_float/fast_float.h"
+#include <iostream>
+#include <string>
+#include <system_error>
+
+template <typename UC> bool test(std::string s, double expected) {
+  std::basic_string<UC> input(s.begin(), s.end());
+  double result;
+  auto answer =
+      fast_float::from_chars(input.data(), input.data() + input.size(), result);
+  if (answer.ec != std::errc()) {
+    std::cerr << "parsing of \"" << s << "\" should succeed\n";
+    return false;
+  }
+  if (result != expected && !(std::isnan(result) && std::isnan(expected))) {
+    std::cerr << "parsing of \"" << s << "\" succeeded, expected " << expected
+              << " got " << result << "\n";
+    return false;
+  }
+  return true;
+}
+
+int main() {
+  if (!test<char>("4.2", 4.2)) {
+    std::cout << "test failure for char" << std::endl;
+    return EXIT_FAILURE;
+  }
+
+  if (!test<wchar_t>("4.2", 4.2)) {
+    std::cout << "test failure for wchar_t" << std::endl;
+    return EXIT_FAILURE;
+  }
+
+#ifdef __cpp_char8_t
+  if (!test<char8_t>("4.2", 4.2)) {
+    std::cout << "test failure for char8_t" << std::endl;
+    return EXIT_FAILURE;
+  }
+#endif
+
+  if (!test<char16_t>("4.2", 4.2)) {
+    std::cout << "test failure for char16_t" << std::endl;
+    return EXIT_FAILURE;
+  }
+
+  if (!test<char32_t>("4.2", 4.2)) {
+    std::cout << "test failure for char32_t" << std::endl;
+    return EXIT_FAILURE;
+  }
+
+  std::cout << "all ok" << std::endl;
+  return EXIT_SUCCESS;
+}