How tests simplify code

Our tests are sometimes giving us pain. But if we listen carefully and have enough design options up our sleeve they can point us in the direction of production code simplification. Links to cognitive psychology.

Transcript

1. Tests - simplificateur de code? Johan Martinsson @johan_alps changit.fr
2. Exceptions! exceptionalMethod(userId, data) { try { let isOwner try { isOwner = this.authservice.isOwnerOf(userId, data.id) } catch (e) { this.logger.error('got http exception while invoking authService') } if (isOwner) { this.dao.update(data.id, data) } } catch (daoException) { this.logger.error('exception caught') } } nonExceptionalMethod(userId, data) { let isOwner = this.authservice.isOwnerOf(userId, data.id) if (isOwner) { this.dao.update(data.id, data) } }
3. l’angoisse de null function printItemNames(data) { if (data.prop) { if (data.prop.cart) { if (data.prop.cart.getList() !== null && data.prop.cart.getList() !== undefined) { for (let listItem of data.prop.cart.getList()) { if (listItem.description) { if (listItem.description.name) { console.debug('Phew, finally here!') // actual business logic console.log('And the item name is... ' + listItem.description.name) } } } } } } } function printItemNames(data) { for (let listItem of data.prop.cart.getList()) { console.debug('Phew, finally here!') // actual business logic console.log('And the item name is... ' + listItem.description.name) } }
4. Conditions function conditionalMethod(data) { if (data.something === 'val') { doSomething() if (data.age <= 40 || 'toto' !== data.something) { doAThirdThing() } else { doSomethingAdditional() } } }
5. Conditions, quand on aime … function conditionalCode(data) { if (data.prop) { if (data.prop.service) { if (data.prop.service.getList() === null && data.prop.service.getList().size > 0) { return 'processed ' + data.prop.service.getList().length + ' results' } else { let defaultResult = 'waiting' return defaultResult; } } } }
6. Duplication registerEmail(person) { if (person.age < 13) { throw new Error('too young') } if (person.name === null) { throw new Error('person must have name') } if (person.email.indexOf('@') <= 0) { throw new Error('invalid email') } console.log('do some stuff') this.dao.insertPerson(person) } registerMobile(person) { if (person.age < 13) { throw new Error('too young') } if (person.name === null) { throw new Error('person must have name') } if (this.hasNonDigits(person.phoneNumber)) { new Error('invalid phone number') } console.log('do some stuff') this.dao.insertPerson(person) } hasNonDigits(phoneNumber) { return /[^\d]+/.test(phoneNumber) }
7. Arguments indirects updateCartItems() { let httpSession = HttpSession.getInstance() let rawCart = httpSession.getCookie().getValue('cart') let cart = new Cart(rawCart) if (cart.lastModificationDate < Date.now() - 24 * 60 * 60 * 1000) { cart.removeAllItems(); } // etc ... // heavy logic to make sure availability is still ok, // that prices haven't changed // that items in the cart haven't expired etc }
8. Service injection, injection, injection … "Chaque nouvelle dépendance doit être passée sur toute la callstack" NOT Injection par constructeur - un seul endroit
9. Code inspectable function hardToTest() { let data = getStuffFromWebservice() // // pure logic // pure logic // pure logic // pure logic // pure logic // pure logic // pure logic // pure logic // pure logic // let result let saveResult = saveToDatabase(result) } function easyToTest() { let data = getStuffFromWebservice() let result = easyToTestPureFunction(data) let saveResult = saveToDatabase(result) } function easyToTestPureFunction(data) { // // pure logic // pure logic // pure logic // pure logic // pure logic // pure logic // pure logic // pure logic // pure logic // }
10. Améliore-t-on le code?
11. Avec tests on a la possibilité de simplifier le code
12. Cercle vicieux/ vertueux
14. “Sometimes we find it difficult to write a test … this usually means that our design can be improved” - S. Freeman, N. Pryce “The tests are a canary in coal mining revealing by their distress the presence of evil design vapors” - Kent Beck
16. TDD requiert une maîtrise cognitive Etat préalable? Action? Résultat attendu?
17. Chunking
18. Mémoire court terme
19. Mémoire long terme Gael Varoquaux flickr Attribution 2.0 Generic (CC BY 2.0)
20. Notre cerveau a besoin de Blocs de 4-5 éléments noms cohésion assembler plutôt que modifier
21. Notre code de prod a besoin de peu de duplication peux de couplage morceaux à assembler BugsZero
22. Les tests ont besoin de être rapides Petites choses Responsabilités séparés Isolation des dépendances
23. Laissons les tests nous aider dans la quête du bon design Ayons zéro tolérance pour des mauvais tests
24. ? @johan_alps changit.fr Tom Mullen (cognitive psychology) Michael Feathers (synergy between testablity and good design)