Nested Unit Tests - An Anti-Pattern

README.md

Nested Unit Tests: An Anti-Pattern

This is an example of what I'm talking about in my 3 minute podcast here

flat.js

import test from 'ava'

import Customers from './Customers'
import getMockCustomers from './Customers/mocks'

test('getCustomers: should return the existing customers', t => {
  const mockCustomers = initializeCustomers()
  const customers = Customers.getCustomers()
  t.deepEqual(customers, mockCustomers)
  cleanupCustomers()
})

test('setCustomers: should set the customers array', t => {
  initializeCustomers([])
  const mockCustomers = getMockCustomers()
  Customers.setCustomers(mockCustomers)
  const customers = Customers.getCustomers()
  t.deepEqual(customers, mockCustomers)
  cleanupCustomers()
})

function initializeCustomers(initialCustomers = getMockCustomers()) {
  Customers.setCustomers(initialCustomers)
  return initialCustomers
}

function cleanupCustomers() {
  Customers.setCustomers([])
}

nested.js

import Customers from './Customers'
import getMockCustomers from './Customers/mocks'

describe('Customers', () => {

  let mockCustomers

  beforeEach(() => {
    Customers.setCustomers([]) // initialize to empty for most tests
    mockCustomers = getMockCustomers() // have mock customers available
  })

  afterEach(() => {
    Customers.setCustomers([]) // clean up just in case
  })

  describe('getCustomers', () => {
    beforeEach(() => {
      Customers.setCustomers(mockCustomers)
    })

    it('should return the existing customers', () => {
      const customers = Customers.getCustomers()
      expect(customers).to.be.eql(mockCustomers)
      // questions you must ask if you're not familiar with this file and it's bigger:
      // - where does `mockCustomers` come from?
      // - what make `getCustomers` return the mockCustomers?
    })
  })

  describe('setCustomers', () => {
    it('should set the customers array', () => {
      Customers.setCustomers(mockCustomers)
      const customers = Customers.getCustomers()
      expect(customers).to.be.eql(mockCustomers)
      // question you must ask if you're not familiar with this file and it's bigger:
      // - where does `mockCustomers` come from? What is it initialized as?
    })
  })
})