Testing event emitted from child component with Vitest & Vue-Test-Utils - vuejs3

Question

I want to test if "onLogin" event emitted from child component will trigger "toLogin" function from parent correctly.
Login.vue
<template>
<ChildComponent
ref="child"
#onLogin="toLogin"
/>
</template>
<script>
import { useAuthStore } from "#/stores/AuthStore.js"; //import Pinia Store
import { userLogin } from "#/service/authService.js"; // import axios functions from another js file
import ChildComponent from "#/components/ChildComponent.vue";
export default {
name: "Login",
components: {
ChildComponent,
},
setup() {
const AuthStore = useAuthStore();
const toLogin = async (param) => {
try {
const res = await userLogin (param);
AuthStore.setTokens(res);
} catch (error) {
console.log(error);
}
};
}
</script>
login.spec.js
import { describe, it, expect, vi, beforeAll } from 'vitest';
import { shallowMount, flushPromises } from '#vue/test-utils';
import { createTestingPinia } from "#pinia/testing";
import Login from "#/views/user/Login.vue"
import { useAuthStore } from "#/stores/AuthStore.js";
describe('Login', () => {
let wrapper = null;
beforeAll(() => {
wrapper = shallowMount(Login, {
global: {
plugins: [createTestingPinia({ createSpy: vi.fn })],
},
});
})
it('login by emitted events', async () => {
const AuthStore = useAuthStore();
const loginParam = {
email: 'dummy#email.com',
password: '12345',
};
const spyOnLogin = vi.spyOn(wrapper.vm, 'toLogin');
const spyOnStore = vi.spyOn(AuthStore, 'setTokens');
await wrapper.vm.$refs.child.$emit('onLogin', loginParam);
await wrapper.vm.$nextTick();
await flushPromises();
expect(spyOnLogin).toHaveBeenCalledOnce(); // will not be called
expect(spyOnStore).toHaveBeenCalledOnce(); // will be called once
})
}
I expected both "spyOnLogin" and "spyOnStore" will be called once from emitted event, however, only "spyOnStore" will be called even though "spyOnStore" should only be called after "spyOnLogin" has been triggered.
The error message is:
AssertionError: expected "toLogin" to be called once
❯ src/components/__tests__:136:24
- Expected "1"
+ Received "0"
What do I fail to understand about Vitest & Vue-Test-Utils?

Answer 1

You shouldn't mock your toLogin method because its part of Login component which you are testing. Therefore, instead of expecting if toLogin has been called, you should check if instructions inside are working correctly.
In your case i would only test if after emit, userLogin and AuthStore.setTokens has been called.