Hi,
One of the problems with mocks, as far as I can tell, is that they
might go out of sync with the real object they're mocking. Is it
possible and sane to detect this by running each spec against its
corresponding mock? Does anyone already do this?
For example: your Account object has a particular behavioural
specification; you perhaps have some convenient helper method for
creating a mock Account which conforms to that specification with
various stubbed responses; and the specifications of other objects use
that mock Account when describing behaviours which involve interaction
with Accounts. What happens when you want to change the behaviour of
Account? Naively, you update the specification and implementation of
Account, your specs all pass, and you think you're done, except you're
not: the Account mock is now misrepresenting the behaviour of Account
all over the system, with the result that you've got failures that the
specs don't reveal.
Of course you have integration tests that will show these failures at
a higher level but it doesn't feel fundamentally like a problem that
RSpec has no business solving. Why not establish a base case for
RSpec's inductive demonstration of correctness by running the Account
spec against the standard Account mock? That way you'll automatically
be told, by RSpec, whenever the actual behaviour of your mock doesn't
match the specified behaviour of the mocked object, and you can let
your integration tests concentrate on the hard stuff (stateful
interactions between many objects) instead of checking that you
haven't forgotten to keep your specs up-to-date.
This assumes a priori that it makes engineering sense to have a
globally-available DRY mock helper for each object (i.e. class) rather
than building up your mocks piecemeal in every spec; I've found that I
always start off a project by doing the latter but end up refactoring
into the former once I get sick of mocking the same stuff over and
over again. Maybe that's the wrong way to do things altogether, or
maybe this is a process issue that I've misunderstood (i.e. the answer
is always to use integration tests to detect this kind of failure), so
stop me if I'm being stupid.
Cheers,
-Tom
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