How to test HOC using react testing library

Question

I have a HOC, adding some props to the component, for handling network requests and passing down data as prop. The following is a very simplified version of the HOC:

export const withTags = (Component) => {
  class WithTags extends PureComponent {
    getItems() {
      return getTags({
            search: this.state.searchTerm
          })
        .then((items) => this.setState({
          items
        }));
    }

    .
    .
    .

    render() {
      return (
        <Component
          {...this.props}
          items={this.state.items}
          getItems={this.getItems}
        />
      );
    }
  }

  return withTags;
}

Using enzyme I can easily do something like:

    it('should return tags', async () => {
      const mockComponent = jest.fn(() => null);
      const WithTagsComponent = withTags(mockComponent);

      const wrapper = shallow(<WithTagsComponent />);
      const res = await wrapper.props().getItems();

      expect(res).toEqual(getTagsResponseMock);
      expect(tagsApi.getTags).toHaveBeenCalledTimes(1);
      expect(tagsApi.getTags).toHaveBeenCalledWith({
        limit: PAGE_SIZE,
      });
      expect(wrapper.props().items).toEqual([tagFlowMock]);
    });

But this approach won't work in React Testing Library, as we should test from the end-user's perspective, and not access props. So, how should I test such HOCs using React Testing Library?

React Testing Library, yes, generally works by interacting with the component under test like a user or other components would. Seems you need to make a mock component that consumes the items and getItems props and does something testable, i.e. some interaction like displaying the items and clicking a button to get new items. Can you provide a more complete HOC code example? — Drew Reese
– Drew Reese, Commented Feb 5, 2021 at 16:22

apieceofbart · Accepted Answer · 2021-02-05 17:38:55Z

I think your test almost works fine but you need to replace two things. Since you're manually calling getItems here you could create a mock Component that would ideally do similar stuff as the components you plan to use with your HOC. For example, this mock component coould have a button that when clicked would call getItems and would also display items.

const MockComponent = ({items, getItems}) => { 
  return (
    <div>
      <button data-testid="button" onClick={getItems}>Click me</button>
      <ul>
        { items.map((item, index) => <li key={index}>{item}</li>) }
      </ul>
    </div>
  )

Then in your test instead of manually calling getItems:

const res = await wrapper.props().getItems();

you could do something like

fireEvent.click(getByTestId('button')

and then assert that your tagsApi was called and that your component displays correct items.

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