Unit testing with Jest

• Jest is one of many JavaScript unit testing frameworks.
• Others include
  • Mocha
  • Ava
• Simple to set up.
  • npm install jest --save-dev
• Simple to run
  • npm test (if you set up package.json correctly)
  • npx jest will run all test files it can find (alternatively ./node_modules/.bin/jest)
  • ./node_modules/./bin/jest name_of_file will test a specific file.
• Walk through Toy.test.js
  • Notice that you can use either it or test
  • Notice the . vs # convention.
  • Notice toMatch for Strings.
• Walk through MemoryToyDB.test.js
  • Notice toBeTruthy (not null, not undefined, not empty string, etc.)
  • Notice toEqual to compare objects.
• Matchers
  • toBe exact equality
  • toEqual recursive equality of arrays and objects.
  • null and undefined are different.
  • toBeTruthy and toBeFalsy
  • toContain for iterable objects.

Mocking / Testing Controllers

• Testing controllers is more of an integration test.
  • You are mostly verifying that the correct methods are called with the correct parameters.
  • Sometimes there is logic to unit tests, sometimes there isn’t.
• When testing controllers, we want to mock the model and view
  • Make sure they are called properly, but we don’t actually want to run the model/view code.
• Walk through ToyController.test.js
  • Notice jest.mock('../Toy');
  • beforeEach
  • the mock of allToys simply produces a local list of toys (rather than hitting the DB).
  • req and res are mock objects passed to the controller methods. (mocks so we can spy on how they are used.)
  • in the #index test, notice how the use of mocks lets us verify that we are correctly passing the value returned by allToys to the templating engine.
  • Notice the use of async when testing functions that use await.
• Other tricks
  • test.only to temporarily one one test only.
  • Testing callbacks: https://jestjs.io/docs/asynchronous