Slow, long running test suites can be almost as dangerous to a project's health as not having tests at all. The presence of tests gives developers, managers and customers a sense of security about the stability of the code base, but that sense of security is only valid if those tests are running (and passing) frequently – preferably continuously. When test suites take too long to run, they cause a productivity drain to the developers, costing us and our customers money. When this productivity drain gets bad enough, developers tend to react to it by avoiding running the test suites, eliminating much of their value. That's why it's very important for project teams to keep their test suites performing quickly.
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