Do you remember projects when your tests run for 30 minutes or even an hour? I do, actually it's nearly turning into a standard. So when CI send you notification that something went wrong, you are already working on a new task, so you have to switch context to fix the stupid bug and then switch context back ... pretty annoying and distracting. Fortunatelly it doesn't have to be so slow, mainly in a web application when you can make a lot of code to run asynchronously since you are always waiting for database ...
Minitest.js in action (it's using colours.js):
NotImplementedError can be sometimes really helpful. Unfortunately rSpec shows them as a failure, but aren't they just the exact equivalent of a pending message?