code: func HTTPSuccessf(t TestingT, handler http.HandlerFunc, method string, url string, values url.Values, msg string, args ...interface{}) bool {
  	if h, ok := t.(tHelper); ok {
  		h.Helper()
  	}
  	return HTTPSuccess(t, handler, method, url, values, append([]interface{}{msg}, args...)...)
  }
docs: // HTTPSuccessf asserts that a specified handler returns a success status code.
  //
  //  assert.HTTPSuccessf(t, myHandler, "POST", "http://www.google.com", nil, "error message %s", "formatted")
  //
  // Returns whether the assertion was successful (true) or not (false).