des mutants dans le code.pdf
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The document discusses mutation testing and provides tips for implementing it. It explains different types of mutations like statement, value, and decision mutations. It also discusses how to calculate mutation score and challenges like cost. Examples are provided using tools like Pitest and Stryker. Advice is given around using mocks, refactoring complex code, and targeting tests to improve mutation testing.
des mutants dans le code.pdf
- 1. Des mutants pour sauver votre code
- 2. SPOILER Beaucoup de références ciné + BD
- 3. Professor X: For someone who hates mutants... you certainly keep some strange company. William Stryker: Oh, they serve their purpose... as long as they can be controlled.
- 5. “the risk of bugs is proportional to the number of possible implementations for your program” https://livebook.manning.com/book/the-joy-of-kotlin/b-property-based-testing-in-kotlin/v-8/14
- 7. Who can you trust?
- 8. ��
- 9. ��
- 10. ��
- 11. Special K
- 12. Special K
- 15. Tester les tests
- 16. Changer pour vérifier Tests: States vs Behaviour Change Behaviour => Test should fail Attention aux doublures de tests
- 18. Qui peut muter ? Tout le monde ? Le code : ● Il doit être résistant ● Toute mutation doit être détectée Les tests ● Ils doivent être fiables ● Les paramètres ?-> Tests paramètrés La configuration.?
- 19. Comment ça marche? • Start with all tests passing Lâchez les fauves! ● Introduce changes in the code and observe the behavior of the unit tests • Two possible outcomes: • Some of the unit tests will start failing : good • All the tests will keep on passing : bad It means that the unit tests do not really validate outcomes of the code under test
- 21. Exemple pour la CLR de .Net // IL ≅ ByteCode, DLL ≅ JAR
- 23. 3 types 1. Statement Mutation – developer cut and pastes a part of a code of which the outcome may be a removal of some lines 2. Value Mutation– values of primary parameters/variables are modified 3. Decision Mutation– control statements are to be changed
- 24. Différents types de mutation ● Arithmetic operators ● Equality operators
- 25. Différents types de mutation ● Logical operators ● Negation operators
- 26. The mutation score is defined as the percentage of killed mutants with the total number of mutants. ● Mutation Score = (Killed Mutants / Total number of Mutants) * 100 Test cases are mutation adequate if the score is 100%. Experimental results have shown that mutation testing is an effective approach for measuring the adequacy of the test cases. But, the main drawback is that the high cost of generating the mutants and executing each test case against that mutant program. https://www.guru99.com/mutation-testing.html
- 28. A vous de jouer! https://pitest.org/ https://stryker-mutator.io/
- 29. A vous de jouer! C# (Stryker.Net) ● 3 branches (complexité croissante) https://github.com/guillaumeagile/CSharp_mutation_Kata JAVA (PiTest) ● problème des Mocks https://github.com/guillaumeagile/mutate-test-kata/tree/onlyMockPb ● comment trouver le bon nombre de tests (nécessaires et suffisants) ? https://github.com/guillaumeagile/mutate_test_kata_java_2
- 30. Comment soigner une mutation (facilement) ? 1. Pas (assez) de test 2. Assertions faibles 3. Cas aux limites
- 31. Freinez vos Minions Mind the false positives • Due to aggressive mutations: • DEFAULTS should be conservative enough • ALL is probably too aggressive
- 32. Smells in your Unit Tests 💩 ● No assertions ● Irrelevant assertions ● Use of Mocks ● Expected results are calculated rather than explicitly specified • Test code reuse (that is test logic reuse, test utilities are good) ● Test data reuse ● "Flickering" tests (tests with nondeterministic behavior) -> Threads 🚑 ● Interdependencies between tests (e.g., execution order) ● Long running tests ● @Ignore‘d or commented out tests
- 33. HandsOn Lab Mocks: Friends or foes?
- 34. Mocks: les ennemis des mutants Test qui utilise un mock pour “simplifier/abstraire” FileSystem par exemple Changement de comportement de FileSystem... sans changer les Mocks Les Mutants n’ont rien vu!
- 35. Rappel : doublures de test Article genèse: https://martinfowler.com/articles/mocksArentStubs.html Article intense sur le sujet : https://enterprisecraftsmanship.com/posts/when-to-mock/
- 36. Stub, Mock Très bon article FR https://agilitateur.azeau.com/post/2011/04/12/Pour-en-finir-avec-les-Stubs-et-les-Moc ks
- 37. Behavioral testing with fakes TIP: Testing the test doubles Conseil avisé: https://tyrrrz.me/blog/fakes-over-mocks
- 38. ICalculate::Variation(prix, delta) : prix Calcultator :: Variation(prix, delta) => prix * delta Mock<Calcultator> . setup(prix, delta) => prix * delta
- 39. ModulateurDePrix(ICalculate calculator){ val delta : Int = 42 prixPlafonné(prix) if (calculator.Variation(prix, delta) < prix ) prix = prix + calculator.Variation(prix, delta) return prix }
- 40. Test::: sut = ModulateurDePrix(mockedCalc, ()-> true) mockedCalc = Mock<Calcultator>() . setup(prix, delta) => prix * 0,2 val actual = sut.prixSelonLeTemps(10) actual shouldBe 12
- 41. Test::: CalculateurQuantique sut = CalculateurQuantique actual = sut.Variation(10, 2) actual shouldBe 2 Code::: Calcultator :: Variation(prix, delta) => prix * delta
- 42. Test::: CalculateurQuantique sut = CalculateurQuantique actual = sut.Variation(10, 2) actual shouldBe 2 Code::: Calcultator :: Variation(prix, delta) => - (prix * delta) MUTATION
- 43. Cas plus épineux https://github.com/tpierrain/NFluent/blob/afda06c1bf761b598a0eaa32f4646510a56f6729/src/NFluent/Helpers/StringDifferen ce.cs#L114 This method has such cyclomatic complexity as well as overlapping conditions that many mutants are able to survive. // original line 131 var boolSingleLine = actualLines.Length == 1 && expectedLines.Length == 1; ... // mutant var boolSingleLine = actualLines.Length == 1 || expectedLines.Length == 1; actualLines et expectedLines ont *dans les faits* la même valeur, aucun test ne peut échouer 😣 https://many-cores.com/2019/05/17/mutation-testing/
- 44. Refactoring needed Ne cédez pas à la tentation de marquer un faux positif the flow was objectively so complex that I could no longer understand, lest anticipate the impact of any change (link to original code). So I refactored it toward a simpler and cleaner design (new version here). Conseils et exemples de @Cyrdup
- 46. Bénéfices de la mutation à vous de me dire...
- 47. Des mutants pour surveiller votre style 1. Petits Pas 2. No Excuses 3. Commencer par un test Rouge!.. 4. ... et pour la bonne raison !! 5. Chicago School of Thought TDD (Inside Out/Bottom Up/Classic)
- 48. Hardcore TDD The process should be: 1. Write the interface 2. Write the tests 3. Write the implementation and check if the tests pass. 4. Refactoring
- 49. So, the first thing you have to do before even starting coding (the tests) is think about the problem in terms of the properties that should verify when considering the input and the output of the function. Property Based Testing = anti mutant weapon ?
- 50. Conseils & REX
- 51. Comment démarrer? Mieux vaut partir de 0
- 52. Cibler le code Uniquement votre code Chassez les dépendances ● en excluant de la mutation ● par une architecture en onion/ hexagonale Du code sans effet de bords ● transparence référentielle ● immutabilité
- 53. Découper le code pour cibler https://www.kennethlange.com/functional-core-imperative-shell/
- 54. Attention aux tests ● Exécution parallèle ● Mutation testing is a computationally expensive process and can take quite some time depending on the size of your codebase and the quality and speed of your test suite. ● Use filters to target only those packages or classes that are currently of interest ● Différence dans les tests = différence dans la résolution des mutations ○ Ex: tests have a hidden order dependency that is not revealed during the normal test run ● Some teams have very slow exhaustive tests or performance tests => EXCLUDE ● Throwing away tests is a hygienic move
- 55. Merci pour vos retours https://roti.express/r/ag21-025