如何对 Vue 应用程序中的嵌套操作进行单元测试？

Question

I have a TypeScript-based Vue project with Jest as a test framework. I have Actions in a Module which I am trying to test.

My Actions look like this:

  @Action({})
  saveSomeData (payload: any): Promise<any> {
    const { isActive, id, routes } = payload
    return this.context.dispatch('otherModule/createId', '', { root: true })
        .then((id: string) => {
          payload = { isActive, id, routes, type: 'postRoutes' }
          return this.context.dispatch('submitRoutes', payload)
        })
  }

  @Action({})
  submitRoutes (payload: any): Promise<any> {
    const { isActive, id, routes, type } = payload
    return ActiveService.setActive(id)
        .then(() => this.context.dispatch(type, { id, routes }))
  }

Here is how my test looks like:

// Mocking createId in otherModule module to return ID
jest.mock('@/store/modules/otherModule', () => ({
  createId: jest.fn(() => Promise.resolve([
    {
      id: 'someId'
    }
  ]))
}))

...

describe('Testing save MyModule data', () => {
    let store: any

    beforeEach(() => {
      store = new Vuex.Store({
        modules: {
          myModule,
          otherModule
        }
      })
    })

    test('Should call createId and then call submitRoutes if ID is empty', async () => {
      const payload = {
        isActive: true,
        id: '',
        routes: []
      }
      const pld = {
        isActive: true,
        id: 'someId',
        routes: [],
        type: 'postRoutes'
      }

      store.dispatch = jest.fn()
      await store.dispatch('myModule/saveSomeData', payload)
      expect(store.dispatch).toHaveBeenCalledWith('myModule/saveSomeData', payload)
      expect(store.dispatch).toHaveBeenCalledWith('otherModule/createId') // <-- here I get an error
      expect(store.dispatch).toHaveBeenCalledWith('myModule/submitRoutes', pld)
    })
  })

Problem: My test fails and I haven't found any way to make it work.

The error:

Error: expect(jest.fn()).toHaveBeenCalledWith(...expected)

Expected: "otherModule/createId"
Received: "myModule/saveSomeData", {"id": "", "isActive": true, "routes": []}

Number of calls: 1

What I've tried

I've followed the Vuex documentation together with Jest , I also tried different solutions from the internet - unfortunately no luck.

I would appreciate any help.

Answer 1

store.dispatch = jest.fn() makes dispatch function a no-op, it isn't expected to call saveSomeData and, therefore, dispatch other actions.

This assertion isn't useful because it basically tests the previous line:

expect(store.dispatch).toHaveBeenCalledWith('myModule/saveSomeData', payload)

store.dispatch spy or stub isn't supposed to affect context.dispatch in actions because the context is created on store initialization and already uses original dispatch . It may be unnecessary to do this because these are actions that should be tested, not Vuex itself.

Actions can be spied on module level with jest.mock and jest.requireActual , or locally on Vuex module object if necessary. Module spies and mocks should happen on top level. Object spies and mocks should happen prior to store instantiation.

In this case a tested units are myModule actions, ActiveService.setActive and otherModule/createId can be considered different units and should be mocked. If postRoutes contains side effects, they can be mocked as well.

jest.spyOn(otherModule.actions, 'createId');
jest.spyOn(ActiveService, 'setActive');
store = new Vuex.Store(...)

...

otherModule.actions.createId.mockValue(Promise.resolve('stubbedId'));
ActiveService.setActive.mockValue(Promise.resolve());
await store.dispatch('myModule/saveSomeData', payload)
// assert otherModule.actions.createId call
// assert ActiveService.setActive call
// assert otherModule.actions.postRoutes call