How do I apply the same test suite to two different target objects?

[AlexanderM (Alexander Momchilov)]

I have written a mock implementation (MockFoo) of a slow/expensive dependency (ProdFoo), that will see heavy use in the tests of several dependent components.

Unfortunately, MockFoo isn't trivial, so I wrote some unit tests for it. However, I wrote those unit tests from my (potentially wrong) understanding of ProdFoo behavior, so I have no certainty that these tests are an accurate reflection of ProdFoo. So naturally, I would like to test my ProdFoo with the same test suite, to ensure that MockFoo accurately mocks ProdFoo.

How can I do that in Swift? Is this approach even a good idea?

[SDGGiesbrecht (Jeremy David Giesbrecht)]

I recommend some variation on this:

Swift-checkit: A library for validating common protocol semantics

I adopted this pattern years ago. Whenever I write a protocol that I expect clients to conform to, then I enclose all its tests in such generic functions in a separate module provided alongside the main one. (Same for classes that will be subclassed.) Then my actual test targets simply call the test functions for each provided concrete conformer and nothing more. That way clients can apply the same set of tests with a single line, and automatically benefit from any new regression or edge case te…