code: func InEpsilon(t TestingT, expected, actual interface{}, epsilon float64, msgAndArgs ...interface{}) bool {
  	if h, ok := t.(tHelper); ok {
  		h.Helper()
  	}
  	actualEpsilon, err := calcRelativeError(expected, actual)
  	if err != nil {
  		return Fail(t, err.Error(), msgAndArgs...)
  	}
  	if actualEpsilon > epsilon {
  		return Fail(t, fmt.Sprintf("Relative error is too high: %#v (expected)\n"+
  			"        < %#v (actual)", epsilon, actualEpsilon), msgAndArgs...)
  	}
  
  	return true
  }
docs: // InEpsilon asserts that expected and actual have a relative error less than epsilon