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0 pointsmikekchar6y ago0 comments

> Classic TDD dogma says to mock super close to the unit under test, so that the only logic in play is the logic within that unit.

I suppose it depends on your definition of "classic TDD dogma". Mocking really wasn't a thing until TDD had been around for about 5-10 years, so super classic TDD dogma has always been "don't mock" ;-)

"London School", GOOSE, Outside-in approach has always been to mock heavily. I call it "wish based programming". You write a test, wishing that you had some facility and since you don't have it, you mock it. Then once the test is in place, you can write your code and eventually write production code that represents the mock (and personally, I remove the mock at that point).

It was really after that, as far as I can tell, that people started to get the idea that you should mock all your collaborators in order to isolate your units. This kind of isolation was never a thing originally (see Kent Beck's original book on the subject). Even if you watch DHH's conversations with Kent Beck (and I think Martin Fowler???) on the topic and they state pretty clearly that "Chicago School" is to avoid mocking except as a last resort (my own personal preference as well). Also take a look at Michael Feather's discussion in his Legacy Code book for a good description of what the original ideas what fakes, stubs and mocks were. These days those definitions are practically lost.

I'm not sure why there has been this idea that mocking was always a part of TDD, but it definitely is a popular notion.

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EdSharkey6y ago

Mocking a module's dependencies decouples the module from the dependency modules. To me, that's the payoff of mocking. And mocks only really click for me in the wider scope of "Outside-In"-style TDD.

It's the black box/functional/integration test that exercises the production code from the standpoint of the enduser that proves whether a tested module's dependencies actually satisfy their contracts. Also, the functional tests are the only place that you can discover if DevOps is needed as well prior to deploying into a real test/prod environment. Plus, the functional test captures the user story that we're focused on in a way unit tests cannot, so the functional tests direct the overall work.

I must have those functional tests in place before I do my unit tests. Otherwise, those mocks really are creating a wish-based programming system.

I agree with you that mocking of today is indistinguishable from what Michael Feathers described in his Legacy Code book (which is excellent regardless, BTW.) Mocking today is so easy to express and change and grok with tools like Spock Framework.

mikepurvis6y ago

Interesting, thanks for the history lesson— I feel a bit better about my own stance, which is also largely to mock as a last resort.

Although I've never been a ruby programmer, you're right that I'm influenced by DHH and the ruby community's approach on a lot of these things.

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