code: func HTTPBodyContains(t TestingT, handler http.HandlerFunc, method, url string, values url.Values, str interface{}, msgAndArgs ...interface{}) bool {
  	if h, ok := t.(tHelper); ok {
  		h.Helper()
  	}
  	body := HTTPBody(handler, method, url, values)
  
  	contains := strings.Contains(body, fmt.Sprint(str))
  	if !contains {
  		Fail(t, fmt.Sprintf("Expected response body for \"%s\" to contain \"%s\" but found \"%s\"", url+"?"+values.Encode(), str, body))
  	}
  
  	return contains
  }
docs: // HTTPBodyContains asserts that a specified handler returns a
  // body that contains a string.
  //
  //  assert.HTTPBodyContains(t, myHandler, "GET", "www.google.com", nil, "I'm Feeling Lucky")
  //
  // Returns whether the assertion was successful (true) or not (false).