Mocks

Mocking HTTP calls with Jest

It's easier to mock an import, so we can simply extract fetch calls to a separate file (http.js in this example).

import mockSomething from './mock_something.json'
 
jest.mock('./http')
const http = require('./http')
 
it('should...', () => {
  // given
  http.fetchSomething.mockResolvedValue(mockSomething)
})

Customize mocks with jest-when

This is a dsl library to help a bit with jest mocks. It might be confusing to use "when" in a "given" statement.

import { when } from 'jest-when'
 
when(myMock).calledWith('input').mockResolvedValue(mockSomething)

Localhost mock flags / feature flags

To setup quick flags, we can use url parameters, and return a mocked implementation:

// true if &flag is in the url
const flag = new URL(window.location.href).searchParams.get("flag")) !== null;

Webpack development mode

We can check if we're running the app in dev mode via:

process.env.NODE_ENV === 'development'