How to fix "Cannot read property 'failedExpectations' of undefined"

While running Karma unit tests, you might run into the following error: Uncaught TypeError: Cannot read property 'failedExpectations' of undefined. The cryptic error message might be a pain in the butt to debug, so let me save you some time.

In your tests, look for reassignment of the result variable. You are probably overwriting a variable from Karma, and this is what breaks your tests. In my case, I was assigning this.result in beforeEach, and renaming it to this.promiseResult fixed the error.