How to unit test devExtreme exportDataGrid method using Jest

Question

I'm stuck trying to mock my method which downloads a csv from the devextreme datagrid. I'm stuck trying to mock this part of the function.

saveAs(new Blob([buffer], { type: 'application/octet-stream' }), 
'DataGrid.csv')

I get the error .

(0 , _fileSaver.default) is not a function

How can I mock the saveAs from file-saver in Jest.

Here is my download function and the jest file

const downloadCsv = () => {
  const workbook = new Workbook()
  const worksheet = workbook.addWorksheet('Main Sheet')
  const exportRes = exportDataGrid({
    component: state.gridInstance,
    worksheet: worksheet
  })
  exportRes.then(() => {
    workbook.csv.writeBuffer().then((buffer) => {
      saveAs(new Blob([buffer], { type: 'application/octet-stream' }), 'DataGrid.csv')
    })
  })
}

----------------------------------------------------------------------

import { shallowMount } from '@vue/test-utils'
import downloadComp from '@/components/data-grid/downloadComp'

jest.mock('devextreme/excel_exporter', () => ({
  exportDataGrid: jest.fn(
    () => new Promise((r) => r({ data: { from: { row: 1, column: 1 }, to: { row: 26, column: 8 } } }))
  )
}))

jest.mock('exceljs', () => {
  return {
    Workbook: jest.fn().mockImplementation(() => {
      return {
        addWorksheet: () => {},
        csv: {
          workbook: {},
          worksheet: null,
          writeBuffer: jest.fn(
            () => new Promise((r) => r({ data: { from: { row: 1, column: 1 }, to: { row: 26, column: 8 } } }))
          )
        }
      }
    })
  }
})

jest.mock('file-saver', () => ({ saveAs: jest.fn() }))
describe('Download grid', () => {
  let wrapper

  beforeEach(() => {
    wrapper = shallowMount(downloadComp)
  })

  it('method handleDownload', () => {
    wrapper.vm.downloadCsv()
  })
})

Answer 1

I was able to solve by changing the import on my component to

import FileSaver from 'file-saver'

then using it like so,

 FileSaver.saveAs(new Blob([buffer], { type: 'application/octet-stream' }), 'DataGrid.csv')

Then in the unit test I could just mock the saveAs function like so.

jest.mock('file-saver', () => ({ saveAs: jest.fn() }))