Allow testing of watches created in Setup()

[mamachanko]

As a reconciler author,
I want to express expected watches in my tests
So that I know when I forgot to create a watch to enqueue tracked resources

When my reconciler uses c.TrackAndGet to track a resource, its easy to forget to create a watch in my reconciler's Setup. I would like to express the expected watches (or lack thereof) through unit tests.

Eventually, I want this to pass

Setup: func(ctx context.Context, mgr ctrl.Manager, bldr *builder.Builder) error {
	bldr.Watches(&source.Kind{Type: &v1.Secret{}}, reconcilers.EnqueueTracked(ctx, &v1.Secret{}))
	return nil
},

and this to fail:

Setup: func(ctx context.Context, mgr ctrl.Manager, bldr *builder.Builder) error {
	return nil
},

I am not even sure there's a case for c.TrackAndGet without its companion watch, or is there?

[scothis]

I haven't found a good fake for the manager and builder resources that would make them unit testable. e2e testing is the preferred approach to date.

It might be worth dealing with the complexity of creating our own fakes since this is a significant part of the controller that isn't unit testable today.