How to mock mixin during unit test using vue-test-utils and jest?

Question

I want to test the testMethod in Test.vue, but testMethod had used mixin which import from App.js.

Test.vue

<script>
    export default {
        methods: {
            testMethod() {
                return 'get'+this.getTestMixin();
            }
        },
    };
</script>

mixins/common.js

export default {
    methods: {
        getTestMixin() {
            return 'test';
        },
    },
};

How to mock the mixin? I tried to mock the mixin like following but failed, any idea where am I doing wrong?

function getTestMixin() {
    return 'test';
}

const localVue = createLocalVue()
localVue.mixin(getTestMixin)

const wrapper = shallowMount(Test, {
    localVue,
})

error message is like following:

TypeError: Cannot read property 'props' of undefined
  46 | beforeEach(() => {
> 47 |  wrapper = shallowMount(Test, {
     |          ^
  48 |      localVue,
  49 |  });
  50 | });

Answer 1

Mixins can be mocked if they are replaced before shallow mount. Something like:

const localVue = createLocalVue();

const mockMixin = {
  methods: {
    mixinMethod() {
        return 'test';
    },
  }
}

const MockedTestComponent = { ...TestComponent, mixins: [mockMixin] };

const wrapper = shallowMount(MockedTestComponent, {
  localVue,
});

expect(wrapper.vm.mixinMethod()).toEqual('test');