Jest unit testing a function that calls a function returning a Promise

Question

I have a function that calls a function that returns a Promise. Here is the code for it:

export const func1 = ({
  contentRef,
  onShareFile,
  t,
  trackOnShareFile,
}) => e => {
  trackOnShareFile()
  try {
    func2(contentRef).then(url => {
      onShareFile({
        title: t('shareFileTitle'),
        type: 'application/pdf',
        url,
      })
    }).catch(e => {
      if (process.env.NODE_ENV === 'development') {
        console.error(e)
      }
    })
    e.preventDefault()
  } catch (e) {
    if (process.env.NODE_ENV === 'development') {
      console.error(e)
    }
  }
}

And func2 that is called in func1 is something like this:

const func2 = element => {
  return import('html2pdf.js').then(html2pdf => {
    return html2pdf.default().set({ margin: 12 }).from(element).toPdf().output('datauristring').then(pdfAsString => {
      return pdfAsString.split(',')[1]
    }).then(base64String => {
      return `data:application/pdf;base64,${base64String}`
    })
  })
}

Now I am trying to write some unit tests for func1 but getting some issues. What I have done so far is this:

describe('#func1', () => {
  it('calls `trackOnShareFile`', () => {
      // given
      const props = {
        trackOnShareFile: jest.fn(),
        onShareFile: jest.fn(),
        shareFileTitle: 'foo',
        contentRef: { innerHTML: 'hello world' },
      }
      const eventMock = {
        preventDefault: () => {},
      }
      // when
      func1(props)(eventMock)
      // then
      expect(props.trackOnShareFile).toBeCalledTimes(1)
    })
    it('calls `onShareFile` prop', () => {
      // given
      const props = {
        trackOnShareFile: jest.fn(),
        onShareFile: jest.fn(),
        shareFileTitle: 'foo',
        contentRef: { innerHTML: 'hello world' },
      }
      const eventMock = {
        preventDefault: () => {},
      }
      // when
      func1(props)(eventMock)
      // then
      expect(props.onShareFile).toBeCalledTimes(1)
    })
  })

Now the first test pass but for the second test I get Expected mock function to have been called one time, but it was called zero times.. I am not sure how to correctly test that. Any kind of help is appreciable.

user_5564305 · Answer

Okay, I've got it working.

First off we need to mock out the data-url-generator(This is from where we import func2). The html2pdf library doesn't work in the testing environment because it is using a fake DOM that doesn't fully implement canvas graphics.

jest.mock('./data-url-generator', () => jest.fn())

Then the test itself can be written like this:

it('invokes the `onShareFile` prop', done => {
    // given
    const t = key => `[${key}]`
    const urlMock = 'data:application/pdf;base64,PGh0bWw+PGJvZHk+PGRpdj5oZWxsbyB3b3JsZDwvZGl2PjwvYm9keT48L2h0bWw+'
    const shareFileTitle = 'bar'
    const contentRef = document.createElement('div')
    contentRef.textContent = 'hello world'
    const trackOnShareFile = () => { }
    const eventMock = {
      preventDefault: () => { },
    }
    func2.mockResolvedValue(urlMock)
    const onShareFileMock = ({ title, type, url }) => {
      // then
      expect(func2).toHaveBeenCalledTimes(1)
      expect(func2).toHaveBeenCalledWith(contentRef)
      expect(title).toBe('[shareFileTitle]')
      expect(type).toBe('application/pdf')
      expect(url).toBe(urlMock)
      done()
    }
    // when
    func1({
      contentRef,
      onShareFile: onShareFileMock,
      shareFileTitle,
      t,
      trackOnShareFile,
    })(eventMock)
  })

Jest unit testing a function that calls a function returning a Promise

1 Answers