Testing often begins with what we hope happens. In my previous article, I demonstrated how to virtualize a service you depend on when processing the “happy path” scenario (that is, testing the outcome of a successful login attempt). But we all know that software fails in spectacular and unexpected ways. Now[he]#039[/he]s the time to take a closer look into how to process the “less happy paths”: what happens when someone tries to log in with the wrong credentials?

Source: LXer – How to test failed authentication attempts with test-driven development