code: func WithinDurationf(t TestingT, expected time.Time, actual time.Time, delta time.Duration, msg string, args ...interface{}) bool {
  	if h, ok := t.(tHelper); ok {
  		h.Helper()
  	}
  	return WithinDuration(t, expected, actual, delta, append([]interface{}{msg}, args...)...)
  }
docs: // WithinDurationf asserts that the two times are within duration delta of each other.
  //
  //   assert.WithinDurationf(t, time.Now(), time.Now(), 10*time.Second, "error message %s", "formatted")