Kent Beck: Composable Tests

Kent Beck distinguishes between test isolation (independent test setup) and test composition (reducing redundant assertions while maintaining predictive power), arguing that composable tests improve maintainability, readability, and speed without sacrificing coverage. By designing tests around orthogonal dimensions rather than copying and extending test cases, organizations can achieve equivalent confidence with significantly fewer tests—reducing the N×M problem from 20 tests to 10 in Beck's interest calculation example. This approach requires thoughtful test design but delivers measurable returns: faster test execution, easier modifications, and improved specificity in failure diagnostics.