CODEWITHSUNDEEP
javascriptnode.jspromisejestjsbabel-polyfill
Frilox
Frilox

Reputation: 855

Jest: resolves return undefined from Promise

I am using jest for testing. I want to test the return of my function:

const xml2js = require('xml2js')

const parser = new xml2js.Parser()

function opmlParser(xmlData) {
  return new Promise((resolve, reject) => {
    parser.parseString(xmlData, (err, data) => {
      if (err !== null && data !== null) reject(err)
      resolve({})
    })
  })
}

The promise resolves {} in order to be in simple test case.

So, I want to test to following function, and I expect the result to be a promise containing {}.
I have the following code:

const fs = require('fs');

test('minimal-opml', () => {
  const xmlData = fs.readFileSync('test/opml-parser/opml/test1.opml')
  return expect(opmlParser(xmlData)).resolves.toEqual({})
})

As the Jest documentation say, I shoud use resolves statement before matching result and use return.

But, I got an issue:

TypeError: Cannot read property 'toEqual' of undefined

resolves return undefined, so I can't continue to test values.

I tried to add global.Promise = require.requireActual('promise'), but stills not work.

Do you have any idea what wrong I am doing?

Upvotes: 0

Views: 3840

Answers (2)

Frilox
Frilox

Reputation: 855

The resolves methode is avalaible from 20.0.0+. So it is not already avalable. source

This is why it return undefined.

Upvotes: 3

Mitch Lillie
Mitch Lillie

Reputation: 2407

You have a few issues in checking for an error in the opmlParser function. You want to check if there is an error and reject, else resolve.

Try this (brackets for clarity, and you may need to refine this to your specific case):

if (err !== null) {
  reject(err)
} else {
  resolve({})
}

Upvotes: 2

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