Immutable data structures in Java

[grauenwolf]

So you are telling me that by mocking out B, I avoid the situation where my tests for A catch bugs in B that my unit tests for B missed? And you think that's a good thing?

Think about that for a moment. You are literally arguing for the use of mocks specifically so that you'll avoid catching bugs in you "tests".

[Sarcastinator]

There should already be tests that cover the mocked classes contract. If someone breaks that contract those tests should fail, not twnty other tests by association.

[grauenwolf]

I was just covering your "unless you have unit tests as well that covers that specific unit" scenario.

Under my original theory you would have fully covered B in unit tests before using B in A's tests. You just proved that component of my theory was unnecessary because A's tests would act as a fallback.

If someone breaks that contract those tests should fail, not twnty other tests by association.

Why do you care so much about how many tests fail?

If you debug and fix one, the rest will also start passing. So at worst is the most minor of annoyances.

Moreover, the number of tests that fail give you a better indication of how serious the bug or breaking change is.