Unit test of a javascript fetch function with jest or mocha

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Unit test of a javascript fetch function with jest or mocha

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#1 by (1 votes)

1

I'm starting TDD studies and came across a function like this:

const fetchexample = callback => {
  fetch('/token', {
    method: 'POST',
    body: 'user=teste'
  }).then(res => res.json()).then(json => {
    localStorage.setItem('token', json.access_token)
  }).then(() => callback())
}

But my question is how would we test this function? Since it makes an asynchronous request and I have never worked with this type of test for this type of request? Would anyone have any examples about the subject or article?

javascript tdd jest mocha

asked by anonymous 09.11.2017 / 12:56

1 answer

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score 1 · Accepted Answer

The it gets two arguments. The description and function to run the test. This function can pass an argument, which is a function to execute when the test is finished. It would look like this:

const fetchexample = callback => {
  fetch('/token', {
    method: 'POST',
    body: 'user=teste'
  }).then(res => res.json()).then(json => {
    localStorage.setItem('token', json.access_token)
  }).then(() => callback())
}
it('should test async code', function(done){
  fetchexample(done);
});

Another way to make the API available is to return a promise. but in this case since it's a callback function that you want to test the done is more practical.

Jest Docs on Asynchronous Tests: link