Using enzyme mock function prior to componentDidMount

When it comes to mocking a function of a component using Jest, Enzyme, and React, the process typically involves creating a shallow wrapper of the component and then overloading the function as needed. However, there seems to be an issue where the componentWillMount is called before the function can be overloaded.

One potential solution to this problem is to find a way to mock the function before actually building the component. This would ensure that the function is properly mocked and ready for use when needed.

javascriptreactjsjestjsjsxenzyme

Answer №1

When you make changes to the Component prototype, all instances of that Component will then have access to these modifications:

Component.prototype.load = jest.fn(function(ref) {
  this.setState({ loading: false, notice: {thing: 'thing'} });
});
let wrapper = shallow(<Component />);

Answer №2

If you want to try another method, consider using componentWillMount in your wrapper instance. By setting the load function as jest.fn, you can then trigger componentWillMount from the wrapper instance.

wrapper.instance().load = jest.fn();
wrapper.instance().componentWillMount();
expect(wrapper.instance().load).toHaveBeenCalled();

For a working example, check out this sandbox: https://codesandbox.io/s/6ym0r4z96w

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