EqualProto Matcher

[jaslong]

Protobuf equality doesn't work with the default Equal matcher because protobufs have special fields. The best way to test protobuf equality is using proto.Equal. I'm proposing a simple matcher that uses protobuf.Equal.

Something like this:

// EqualProto succeeds if actual proto matches the passed-in proto.
func EqualProto(message proto.Message) types.GomegaMatcher {
	return &equalProtoMatcher{message: message}
}

type equalProtoMatcher struct {
	message proto.Message
}

func (matcher *equalProtoMatcher) Match(actual interface{}) (bool, error) {
	message, ok := actual.(proto.Message)
	if !ok {
		return false, fmt.Errorf("EqualProto matcher expects a proto message.  Got:\n%s", format.Object(actual, 1))
	}

	return proto.Equal(message, matcher.message), nil
}

func (matcher *equalProtoMatcher) FailureMessage(actual interface{}) string {
	return format.Message(actual, "to equal", matcher.message)
}

func (matcher *equalProtoMatcher) NegatedFailureMessage(actual interface{}) string {
	return format.Message(actual, "not to equal %v", matcher.message)
}

[jaslong]

Related issue regarding time.Time: #264. Both time.Time and protobufs follow the convention of having an Equal method of the form "(T) Equal(T) bool". Thoughts about special casing this form of Equal method?

My team has gotten around this issue by creating a new matcher that uses https://godoc.org/github.com/google/go-cmp/cmp, which special cases the Equal method. Here's a gist: https://gist.github.com/jaslong/8852fb0ae5367484957dc9b6c33924d3

[MasslessParticle]

Why not make the Equals matcher look to see if the given value implements proto.Message, and then use proto.Equal under the hood?

[james-lawrence]

because then protocol buffers becomes a mandatory dependency even if you don't use it.