Mocking a function in jest which returns Promise<string[] | never>

Question

I'm using React+JEST to test an existing component. It has a function filterDeliveries like so :

const filterEmptyDeliveries = (arr): Promise<string[] | never> => {
    if (arr.length === 0) {
      return Promise.reject("empty") as any as Promise<never>
    }
    return Promise.resolve(arr) as Promise<string[]>
  }

In my component I call it like this:

const whiteListArr = []
const setupDeliveryType = async () => {
   const tempAsin = [] // Empty or Not Empty
    try {
       ... other code
      if (tempAsin.length !== 0) {
        if (whiteListArr.length === 0) {
          whiteListArr.push(... some list computed above)
        } else {
          await filterEmptyDeliveries(asinWhiteList)
        }
       } else {
         await filterEmptyDeliveries(whiteListArr)
      } 
    } catch (err) {
      console.log(err)
    } finally {
      setLoading(false)
    }
  }

This is how I'm mocking in my tests

const filterEmptyDeliveries = jest.fn()
filterEmptyDeliveries.mockResolvedValue(['A12334567'])

it('calls setupDeliveryType ', async () => {
      const wrapper = mount(<Component / >)
      await act(flushPromises)
      wrapper.update()
      await act(flushPromises)

      const whiteList = ['B00000000']
      ... other tests that pass so i'm pretty confident the code reaches here
      await act(flushPromises)
      expect(filterEmptyDeliveries).toHaveBeenCalled() // Fails

     /// Fails with
      Expected number of calls: >= 1
      Received number of calls:    0

    })

Where Am I going wrong here?

Answer 1

You are mocking a function called filterDeliveries, but the component is calling filterEmptyDeliveries.