* It would be nice if this was a predicate, so that it's clear that it's a query message that returns true/false rather than a command method (the fact that it starts with `yield_...` makes it sound like a command).
* On `MessageExpectation`, you phrased it as `yield_receiver_to_implementation`, so for consistency, I'm thinking this should be `yield_receiver_to_any_instance_implementation_blocks=` and `yield_receiver_to_any_instance_implementation_blocks?`.  I like using the word `receiver` for the object (rather than using `instance` twice in the name), and it's more accurate to say the receiver is yielded _to_ the block rather than _from_ the block.