Steve Freeman has been involved in automated unit testing basically as long as it has existed (not quite, but close). He was one of the inventers of mocking. He and I have had a number of discussions about mocks and when and how to use them.
Although we disagree, we each respect the other’s positions. In the context of the design approaches that Steve follows, mocks are a great tool and aren’t dangerous. In the design approaches I follow, they are unnecessary and inhibit feedback. So don’t just learn mocking and testing from Steve; also learn about his approaches to designing systems.
I asked Steve the same question that I asked everyone else:
What are the characteristics of a good test suite?
- Expressiveness. I can read any test and understand what point about the code I was trying to make at the time. That also includes being able easily to find the relevant test that answers whatever question I have.
- Confidence. I don’t expect perfect coverage but I do need to feel confident that if the tests pass, the system is pretty much good enough to ship. Otherwise, I have none of the benefits with the downside of all that extra code.
- Fast. Dan Bodart has been doing some interesting work recently on making full, top-to-bottom tests suites for a real application run in seconds. It’s a game changer.
- Separation of concerns. Obviously there will be some overlap between tests, but I shouldn’t have to change too many tests for new features, unless it’s a huge change. Higher-level tests assume that lower-level code works, and don’t try to reproduce all their checking.
- Good diagnostics. When a test fails, the output tells me what went wrong. I don’t have to spend a week with the debugger to figure out what happened.
- Well-tended. I don’t just keeping adding tests, but I regularly review what I have and maintain them to reduce duplication and uncover a domain language. When I’m really doing well, concepts from the tests will move into the production code.
I’m sure I’m missing something screamingly obvious, but that’ll do for now.
Steve’s Unsolicited Follow-up
Damn. I should have just written “what Ward said.”
Love (or hate) that answer? Want to see other answers?