Jest assert promise resolved with object containing

Question

Say I want to test a module that returns a Promise:

function myFunc () {
    return Promise.resolve({
        anArray: [1,2,3,4,5,6]
    })
}

Using Jest, how can I assert the length of the array contained in the object the promise resolves to?

describe('myFunc', () => {
  it('returns array of length 6', () => {
    expect.assertions(1)
    return expect(myFunc()).resolves // ... something here
  })
})

If it were synchronous, I would do something like:

let result = myFunc()
expect(result.anArray.length).toBe(6)

How does this work with Promises?

Answer 1

There are two ways either return the promise from the test and make the assertion in the then or make your test using async/await

describe('myFunc', () => {
  it('returns array of length 6', () => {
    expect.assertions(1)
    return expect(myFunc())
      .then(result =>  expect(result).toEqual([1,2,3,4,5,6]);)
  })
})

describe('myFunc',() => {
  it('returns array of length 6', async() => {
    const result = await expect(myFunc())
    expect(result).toEqual([1,2,3,4,5,6]);)
  })
})

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