Vue-Router Mock With Vue-Test-Utils & Vitest

Question

I'm trying to understand the logic of mocking the Vue-Router with Vitest.

For this, I tried to set up and mock my test environment on a very simple project. When I tried to proceed according to the official documentation of Vue-Test-Utils, I always got an error. I don't know if it's because they use Jest.

Using real vue-router solves my problem but I think it's better to mock vue-router.

Below, I first convey the source codes of the project, and then the error I received.

Home.vue

<script setup lang="ts">
import {onMounted} from "vue";
import {useRoute} from "vue-router";

const route = useRoute()

onMounted(() => {
  console.log(route.query)
})
</script>

<template>
  <div>Home</div>
</template>

Home.spec.ts

import {expect, it, vi} from "vitest";
import {mount} from "@vue/test-utils";

import Home from "../src/components/Home.vue"

it('Home Test', async () => {
    const wrapper = mount(Home)

    expect(wrapper.exists()).toBeTruthy()
})

vite.config.ts

/// <reference types="vitest" />
import { defineConfig } from 'vite'
import vue from '@vitejs/plugin-vue'

// https://vitejs.dev/config/
export default defineConfig({
  plugins: [vue()],
  test: {
    environment: 'jsdom',
    include: ['./test/**/*.spec.ts'],
    exclude: ['node_modules', 'dist'],
    globals: true
  }
})

My error message is as follows:..

Methods I've Tried

I tried to mock vue-router like below

vi.mock('vue-router', () => ({
    useRoute: vi.fn(),
}))

or just

vi.mock('vue-router')

Here is my final Home.spec.ts file

import {expect, it, vi} from "vitest";
import {mount} from "@vue/test-utils";

import Home from "../src/components/Home.vue"

vi.mock('vue-router')

it('Home Test', async () => {
    const wrapper = mount(Home, {
        global: {
            stubs: ["router-link", "router-view"]
        }
    })

    expect(wrapper.exists()).toBeTruthy()
})

Answer 1

First, I expected to see the router-link or router-view in Home.vue:

<script setup lang="ts">
import { onMounted } from 'vue';
import { useRoute } from 'vue-router';

const route = useRoute();

onMounted(() => {
  console.log(route.query);
});
</script>

<template>
  <router-link to="home">Go to home</router-link>
  <router-view />
</template>

So, the Home.spec.ts should be something like this:

import { expect, it, vi } from 'vitest';
import { mount } from '@vue/test-utils';
import * as VueRouter from 'vue-router';
import Home from '../src/components/Home.vue';

describe('./path/to/Home.vue', () => {
  const useRouteSpy = vi.spyOn(VueRouter, 'useRoute');
  const getWrapper = () => mount(Home as any, {
    global: {
      stubs: {
        'router-link': { template: '<div/>' },
        'router-view': { template: '<div/>' },
      },
    },
  });

  it('the component should be mounted', () => {
    // ARRANGE
    const useRouteMock = useRouteSpy.mockImplementationOnce({ query: 'query' });
    // ACT
    const wrapper = getWrapper();
    // ASSERT
    expect(useRouteMock).toHaveBeenCalled();
    expect(wrapper.exists()).toBeTruthy();
  });
});

Some comments/words of advice:

• Use describes to boundary the test context
• Define a global function to mount the component, reuse instead of repeat
• Use .spyOn() and .mockImplementation...() to spy and mock
• Use some structured/straightforward way to write your test, like AAA [arrange, act, assert] or GWT [given, when, then]. I have been testing for a few years and still using it, it helps me to understand what I'm testing
• Use .toHaveBeenCalled...() to check if the mock worked as expected
• The stubs in the mount() function should be related with the components used in the template (so, if you're not using <router-view>, it should not be listed as a stub)

Hope that helps, Cheers!