Originally the class property in question was going to be set in the init method, so I tested for the presence of the property after creating an instance of the relevant class. Easy pass. Weeks later I did something (and forgot to run the test suite). Today I did something else, and this time I did run them. Hey presto, failed test. And completely unexpected, because it was the property exercising one. How on Earth did that happen?

Upon closer inspection I tracked it down to a refactoring, where I extracted some code from init as there were now multiple ways an object could be initialised. The failing code was part of that, and I realised that it was called from the new initFromFile: method, but no longer from the default initialiser. Easy mistake to make. And had I run my test-suite more consistently, my application would not have been with a potential bug in the meantime.

What did I take home from this?

• Even Mickey-Mouse-tests are valuable. No test is too small to be useful (provided it’s actually testing something valid).
• The test-suite should really be run after every change. I’ll have to check if I can get Xcode to run them automatically after each compilation…

Update: Since I stopped doing much iOS or Mac OS work, I no longer used Xcode. And I’m not missing it :)