func setType(ext, typ string) {
	if !strings.HasPrefix(ext, ".") {
		panic("missing leading dot")
	}
	if err := setExtensionType(ext, typ); err != nil {
		panic("bad test data: " + err.Error())
	}
}

func TestTypeByExtension(t *testing.T) {
	once = sync.Once{}
	// initMimeForTests returns the platform-specific extension =>
	// type tests. On Unix and Plan 9, this also tests the parsing