Add test for user-defined types formatting

test/CMakeLists.txt

@@ -108,6 +108,7 @@ add_fmt_test(printf-test)
 add_fmt_test(custom-formatter-test)
 add_fmt_test(ranges-test)
 add_fmt_test(scan-test)
+add_fmt_test(user-defined-type-test)
 
 if (NOT MSVC_BUILD_STATIC)
   add_fmt_executable(posix-mock-test

test/user-defined-type-test.cc

@@ -0,0 +1,43 @@
+#ifndef _CRT_SECURE_NO_WARNINGS
+#  define _CRT_SECURE_NO_WARNINGS
+#endif
+
+#include <algorithm>
+
+#include "fmt/format.h"
+#include "gtest-extra.h"
+
+enum struct color { red, green, blue };
+
+template <> struct fmt::formatter<color> {
+  constexpr auto parse(format_parse_context& ctx) {
+    auto it = ctx.begin();
+    if (it == ctx.end()) throw fmt::format_error("incomplete format string");
+    if (*it != '}') throw fmt::format_error("unknown format specs");
+    return it;
+  }
+  template <typename FormatContext> auto format(color c, FormatContext& ctx) {
+    static const char red_s[] = "red", green_s[] = "green", blue_s[] = "blue";
+    const char *begin_p, *end_p;
+    switch (c) {
+    case color::red:
+      begin_p = std::begin(red_s);
+      end_p = std::end(red_s);
+      break;
+    case color::green:
+      begin_p = std::begin(green_s);
+      end_p = std::end(green_s);
+      break;
+    case color::blue:
+      begin_p = std::begin(blue_s);
+      end_p = std::end(blue_s);
+      break;
+    }
+    return std::copy(begin_p, end_p - 1, ctx.out());
+  }
+};
+
+TEST(UserDefinedTypeTest, Format) {
+  EXPECT_EQ("red green blue",
+            fmt::format("{} {} {}", color::red, color::green, color::blue));
+}