Testing with env vars

To test with different kinds of env vars in different unit tests we need to do the following.

1. set up the vars on process.env.NODE_ENV
2. run the test
3. reset it

Step three is very important since process.env is a global variable, we want to make sure that when every test uses it, it returns what is expected.

setting up vars on process.env.NODE_ENV and running the test

To do this, we write a function which does this for us

const setUpProductionEnv = () => {
  process.env.NODE_ENV = 'production';
}

Then to use it we can either use it in a beforeEach block before certain assertions in a test suite, or at the beginning of a test

describe('Stuff in production', () => {
  beforeEach(() => {
    setUpProductionEnv()
  })
  it('works in production', () => {
    // assert stuff for production
  })
})

it('works in production', () => {
  setUpProductionEnv();
  // assert stuff for production
})

I personally like this approach because it is very clear when the production env is being used.

Reset it

Because process.env.NODE_ENV is global, once we set it somewhere, we should reset it before the next test, otherwise the next test's behaviour might be unexpected.

When you are writing a new test, is no way at the beginning of a test to tell what process.env.NODE_ENV is. Moreover, unless specified manually, there is no way to guarantee that the test suites will run in a certain order., we might test something with an unexpected.

To do this we should create an all-test afterEach block which resets the process.env.NODE_ENV to the default node env (which is just 'test' in jest, if non is specified elsewhere). To do this, we create a file with the following

const DEFAULT_ENV = 'test'

afterEach(() => {
  process.env.NODE_ENV = DEFAULT_ENV;
})

and we connect it to jest by adding it to our jest config's setupFilesAfterEnv property

module.exports = {
  setupFilesAfterEnv: ['<rootDir>/jest-setup/afterEnv.js'],
};