code: func EqualError(t TestingT, theError error, errString string, msgAndArgs ...interface{}) bool {
  	if h, ok := t.(tHelper); ok {
  		h.Helper()
  	}
  	if !Error(t, theError, msgAndArgs...) {
  		return false
  	}
  	expected := errString
  	actual := theError.Error()
  	// don't need to use deep equals here, we know they are both strings
  	if expected != actual {
  		return Fail(t, fmt.Sprintf("Error message not equal:\n"+
  			"expected: %q\n"+
  			"actual  : %q", expected, actual), msgAndArgs...)
  	}
  	return true
  }
docs: // EqualError asserts that a function returned an error (i.e. not `nil`)
  // and that it is equal to the provided error.
  //
  //   actualObj, err := SomeFunction()
  //   assert.EqualError(t, err,  expectedErrorString)