Jest URL.createObjectURL is not a function

Question

I'm developping a reactJs application. I'm using jest to test my application. I want to test a function that download a blob.

But unfortunately I receve this error:

URL.createObjectURL is not a function

my test function:

describe('download', () => {
    const documentIntial = { content: 'aaa' };
    it('msSaveOrOpenBlob should not have been called when navigao is undefined', () => {
      window.navigator.msSaveOrOpenBlob = null;
      download(documentIntial);
      expect(window.navigator.msSaveOrOpenBlob).toHaveBeenCalledTimes(0);
    });
  });

The function I want to test:

export const download = document => {
  const blob = new Blob([base64ToArrayBuffer(document.content)], {
    type: 'application/pdf',
  });
  if (window.navigator && window.navigator.msSaveOrOpenBlob) {
    window.navigator.msSaveOrOpenBlob(blob);
    return;
  }

  const fileURL = URL.createObjectURL(blob);
  window.open(fileURL);
};

Answer 1

This would appear to be as simple as setting up URL on the Global in Jest. Something like

describe('download', () => {
  const documentIntial = { content: 'aaa' };
  global.URL.createObjectURL = jest.fn();
  it('msSaveOrOpenBlob should not have been called when navigao is undefined', () => {
    global.URL.createObjectURL = jest.fn(() => 'details');
window.navigator.msSaveOrOpenBlob = jest.fn(() => 'details');
download(documentIntial);
expect(window.navigator.msSaveOrOpenBlob).toHaveBeenCalledTimes(1);
  });
});

This should result in a test that you can also use for checking if global.URL.createObjectURL was called. As a side note: you may also run into a similar issue with window.open I would suggest mocking that as well if this becomes the case.