Imagine you're building Amazon.com, and you have a rating system. You might not want to show an average rating to the user until there's been some minimum number of ratings. Of course, you'll want to test that that feature works. However, in other tests, you might want to disable that feature by setting the minimum number of ratings required to 0.
More generally, I sometimes run into the situation where I have a constant in my model that I might want to change, but only for a specific test. Instead of using a constant, you can use a class attribute. However, since class attributes aren't part of a database transaction, they don't get reset after every test. That's a problem since one test that changes the class attribute might mysteriously break another test that relies on that class attribute. I had a problem where one feature file would pass when run alone, but it wouldn't pass when all the features files were run. Here's how to make it all wor…