Shortcut for expecting method call with matching arguments & stub calls with non-matching arguments

[floehopper]

See #487 (comment) by @Bennet-Sunder. Maybe something like this:

foo.expects(:bar).with(123).once.but_otherwise_stubs

foo.bar(123) # expected
foo.bar(456) # stubbed
foo.bar('a', 'b', 'c') # stubbed

[floehopper]

My initial thought is that the chained but_otherwise_stubs method goes a bit against the grain of the internal model, because it would need to create a separate Expectation instance rather than just modifying the one from foo.expects(:bar). However, I'm pretty sure it would be possible to implement.

My other concern is whether this is a common enough scenario to make having a shortcut worthwhile. Nobody else has asked for anything similar in over 10 years!