Tips for testing "defineAsyncComponent" in Vue 3:

Question

Tips for testing "defineAsyncComponent" in Vue 3:

Suppose I need to unit test this utility function. I am utilizing Vue 3, however, this code resides in a "regular" JavaScript file rather than an SFC.

How can I go about doing that?

function getDynamicComponent() {
  if (...)  {
    return defineAsyncComponent(() => import('../path/to/component-A.vue'))
  } else {
    return defineAsyncComponent(() => import('../path/to/component-B.vue'))
  }
}

In scenarios like this, my approach is to mock the implementation of functions and verify .toHaveBeenCalledWith(...). But since I cannot do that with import, right?

P.S. Any insights into Jest or Vitest syntax would be greatly appreciated

javascript vue.js unit-testing jestjs vuejs3

Answer 1

Answer №1

If you want to test a specific function using jest, you can mock it like this:

let defineAsyncComponent = jest.fn()

let vueMock = {
    defineAsyncComponent
}

jest.mock('vue', () => {
    return vueMock;
})

import { defineAsyncComponent } from 'vue';

console.log(defineAsyncComponent._isMockFunction) // true

To ensure that defineAsyncComponent was called during your test, you can do the following:

expect(defineAsyncComponent).toHaveBeenCalled()

It's important to note that testing with toHaveBeenCalledWith may be challenging as it uses toEqual and could lead to failed tests.

One approach is to define an implementation for the defineAsyncComponent function in order to test the parameter:

let defineAsyncComponent = jest.fn().mockImplementation((fn) => {
    expect(typeof fn).toBe('function')
})

You could also verify the returned promise value by calling the function, but keep in mind that at this point you are essentially testing the import() function itself rather than adding value to your test:

let defineAsyncComponent = jest.fn().mockImplementation((fn) => {
    expect(typeof fn).toBe('function')
    expect(typeof fn().then).toBe('function')
})

Answer 2

If you want to test a specific function using jest, you can mock it like this:

let defineAsyncComponent = jest.fn()

let vueMock = {
    defineAsyncComponent
}

jest.mock('vue', () => {
    return vueMock;
})

import { defineAsyncComponent } from 'vue';

console.log(defineAsyncComponent._isMockFunction) // true

To ensure that defineAsyncComponent was called during your test, you can do the following:

expect(defineAsyncComponent).toHaveBeenCalled()

It's important to note that testing with toHaveBeenCalledWith may be challenging as it uses toEqual and could lead to failed tests.

One approach is to define an implementation for the defineAsyncComponent function in order to test the parameter:

let defineAsyncComponent = jest.fn().mockImplementation((fn) => {
    expect(typeof fn).toBe('function')
})

You could also verify the returned promise value by calling the function, but keep in mind that at this point you are essentially testing the import() function itself rather than adding value to your test:

let defineAsyncComponent = jest.fn().mockImplementation((fn) => {
    expect(typeof fn).toBe('function')
    expect(typeof fn().then).toBe('function')
})

Tips for testing "defineAsyncComponent" in Vue 3:

Answer №1

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