# Test suite minimization Minimization is the [regression-suite management](https://quality.stereobooster.com/regression-management.md) technique that permanently *removes* tests judged redundant against a criterion, typically coverage. Where several tests cover the same statements, one is kept and the rest are dropped (Yoo and Harman 2012)[^yoo2012]. ## What it does It caps suite growth by discarding coverage-redundant tests for good. The danger is inherent in the criterion. Coverage redundancy is redundancy in the reachability link of the [RIPR chain](https://quality.stereobooster.com/measuring-test-effectiveness.md#why-a-test-catches-a-fault-the-ripr-chain) alone; two tests that execute the same lines can still differ in whether they *infect* and *propagate* state. A test that is redundant for coverage may be the sole detector of a real fault, and deleting it optimizes reachability while throwing that detector away. ## Choosing the criterion The same coverage profile supports opposite decisions. When read as gaps it argues for *adding* tests where code is unexercised; when read as redundancy it argues for *removing* tests that exercise only already-covered code. Minimization is that second reading of the same profile. The profile also marks what is *not* safe to drop: a test that is the sole cover of some statement is not redundant on the criterion, so a coverage-preserving minimizer must keep it. (Formally it is a set-cover problem: the smallest subset of tests whose union still covers every element.) [Mutation testing](https://quality.stereobooster.com/mutation-testing.md) supplies a criterion stronger than coverage: it scores each test by the mutants it kills, and counts a test redundant only when every mutant it kills is also killed by another test. A kill exercises the whole RIPR chain, so mutation-redundancy accounts for the infection and propagation that coverage cannot see, and a test that uniquely kills a mutant is kept even where its lines are covered elsewhere. It costs far more to compute, which is why coverage stays the common criterion despite being the weaker one. ## When to use, when not Prefer [selection](https://quality.stereobooster.com/regression-test-selection.md) (skip a test for this run) over permanent minimization (delete it for good), unless the suite's growth is genuinely unsustainable and the deleted tests are demonstrably redundant, not just coverage-redundant. **Don't minimize a suite to hit a size or coverage target.** Deleting coverage-redundant tests to make a number move is Goodhart's-law gaming, the same failure mode that afflicts [coverage targets](https://quality.stereobooster.com/coverage.md); it buys a smaller suite at the risk of a lost fault detector. ## Classification - **Quality dimensions:** Maintainability (caps suite growth by permanently removing coverage-redundant tests) — permanently removes coverage-redundant tests; it prunes the suite, it does not run or verify it, so it sits off the code-verification axes. - **Area:** Suites whose growth is genuinely unsustainable and whose redundant tests are demonstrably safe to delete. ## Referenced by - [Mutation testing](https://quality.stereobooster.com/mutation-testing.md) · Methods - [Regression-suite management](https://quality.stereobooster.com/regression-management.md) · Methods - [The test suite as an object](https://quality.stereobooster.com/test-suite.md) · Methods ## References [^yoo2012]: Yoo, Shin, and Mark Harman. 2012. "[Regression Testing Minimization, Selection and Prioritization: A Survey](https://coinse.github.io/publications/pdfs/Yoo2010fk.pdf)." *Software Testing, Verification and Reliability* 22 (2): 67–120. . ## Acronyms - RIPR — reachability, infection, propagation, revealability