Testing with Mocks

[mabelleeyanhwa]

code-along template: https://github.com/thoughtworks-jumpstart/learn-mocking-and-stubbing

lesson outline:

• write on board: jest.fn(factory), jest.mock(path, factory)
• what are mocks
  • Mocking is a technique to isolate test subjects by replacing dependencies with objects that you can control. The goal for mocking is to replace something we don’t control with something we do
• when to mock
• how to create mocks with jest.fn() and jest.mock()
• assertions which we can use on mock functions
• demo
  • fetch
  • payment gateway
  • 2 classes

jest gives us many ways to define a mock. see https://medium.com/@rickhanlonii/understanding-jest-mocks-f0046c68e53c for a comparison (note. it's using ES6 import syntax, so you have to map it to your CommonJS import/export syntax)

recap:

• benefits of mocking
  • simplify testing (e.g. new Cat(brain, tail, coatOfFur, owner))
  • prevent expensive operations (e.g. fetch or actual payments)
  • simulate all edge cases in a class/function
  • remove dependencies (on data, network requests, other classes, etc)
• terms
  • mocks, stubs, dummies, spies