One of the benefits of having an automated test suite is the feedback given when the code is being changed. As the project grows, the test suite becomes slower and slower every day, until it’s so slow it stops being useful. Tests are disabled, skipped and finally removed.
A huge part of the problem lies in getting the testing pyramid wrong and putting too much effort into the wrong type of testing. Learn how to structure your project to benefit from lightning fast tests. Apply the right amount of testing on appropriate levels and run your tests in seconds, not hours.