How to prevent "polluting" variables in a Jest test?

Question

My test looks like this:

const aframeViewer = new VRMaker.AframeViewer()
let el
let panoramas
let panorama

beforeEach(() => {
  panorama = { objectId: '1' }
  panoramas = [panorama]
  el = 'vrmaker-aframe'
})

describe('commonViewer', () => {

  it('addPanoramas', () => {
    const oldPanoramas = clone(panoramas)
    aframeViewer.addPanoramas([{ objectId: '2' }])
    expect(aframeViewer.getPanoramas()).not.toBe(oldPanoramas)
  })

  it('getPanoramas', () => {
    expect(aframeViewer.getPanoramas()).toBe(panoramas)
  })

  it('getCurrentPanorama', () => {
    expect(aframeViewer.getCurrentPanorama()).toBe(panorama)
  })
}) 

The problem here is that aframeViewer.addPanoramas([{ objectId: '2' }]) turns this:

[{ objectId: 1 }]

Into this

[{ objectId: 1 }, { objectId: '2' }]

Therefore the getPanoramas test has a polluted variable. (getCurrentPanorama suffers from the same problem.)

What's the best way to avoid these kind of situations?

Answer 1

1. Declare let aframeViewer; and in the beforeEach add:

   aframeViewer = new VRMaker.AframeViewer()

2. Don't count on one test to run before another test, make sure to do whatever you need to do either in beforeEach or at the beginning of the test.