Running irrelevant tests wastes time, energy, and resources.Test-impact analysis (TIA) helps in skipping irrelevant tests based on code dependencies.Automatic TIA methods use static code analysis or run-time coverage to identify dependencies.File dependencies, program dependency graphs, and coverage are key methods used in TIA.Manual specification of dependencies can also be done for TIA, especially for non-code changes.TIA can be complemented with other speed-up methods like test suites, parallelization, and predictive test selection.Predictive selection involves choosing tests likely to fail and can be sophisticated using machine learning models.Test-impact analysis can be beneficial for speeding up test suites and improving efficiency in testing processes.Users are encouraged to try out test-impact analysis tools like spdr for Python to enhance their testing strategies.Efficient testing practices like TIA can improve development productivity and reduce unnecessary testing overhead.