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