The easiest way to avoid brittle tests is to check only the properties you care about. Test your program’s simpler and more stable interfaces in preference to its internal functions. Be selective in your assertions. Don’t check for exact string matches, for example, but look for relevant substrings that will remain unchanged as the program evolves. It’s often worth writing a substantial function to distill a complex output down to its essence so that assertions will be reliable. Even though that may seem like a lot of up-front effort, it can pay for itself quickly in time that would otherwise
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