Add some more new date formatting tests.

- Failures: SupportsCustomFormatWithBrace, SupportsISO8601Format

test/format_test.cxx

@@ -65,3 +65,15 @@ TEST(FormatTest, FormatsMicroseconds) {
   auto fmt = format::parse_format_string("%d");
   EXPECT_THAT(fmt.process({{NOW,123000}}), Eq("2019-04-04 18:17:20,123"));
 }
+
+TEST(FormatTest, SupportsCustomFormatWithBrace) {
+  using testing::Eq;
+  auto fmt = format::parse_format_string("%d{%Y}");
+  EXPECT_THAT(fmt.process({{NOW,0}}), Eq("2019"));
+}
+
+TEST(FormatTest, SupportsISO8601Format) {
+  using testing::Eq;
+  auto fmt = format::parse_format_string("%d{ISO8601}");
+  EXPECT_THAT(fmt.process({{NOW,0}}), Eq("2019-04-04T18:17:20.000Z"));
+}