How to test if a component is rendered with the right props when using react-testing-library?

Question

I have some components that are rendering another component (FetchNextPageButton) that is already tested in isolation, like these ones:

const News = () => (
  <div>
    <h1>News</h1>
    ...
    <FetchNextPageButton query={NEWS_QUERY} path="viewer.news" />
  </div>
)

const Jobs = () => (
  <div>
    <h1>Jobs</h1>
    ...
    <FetchNextPageButton query={JOBS_QUERY} path="viewer.jobs" />
  </div>
)

const Posts = () => (
  <div>
    <h1>Posts</h1>
    ...
    <FetchNextPageButton query={POSTS_QUERY} path="viewer.posts" />
  </div>
)

The thing is that I'd not like having to add tests on each of these components for a functionality that is already tested somewhere else, so I think that should be enough just to test that the component is rendered and that I'm passing the right props to it.

I'd have been able to test this easily with Enzyme with something like this:

expect(wrapper.find('FetchNextPageButton').props()).toMatchObject({
  query: NEWS_QUERY,
  path: "viewer.news"
})

So I'm wondering what's the best approach to test it by using React testing library instead.

Answer 1

This is the approach that Kent C. Dodds (the creator of RTL) shared with me after discussing it with him:

import FetchNextPageButton from 'FetchNextPageButton'

jest.mock('FetchNextPageButton', () => {
  return jest.fn(() => null)
})

// ... in your test
expect(FetchNextPageButton).toHaveBeenCalledWith(props, context)

Answer 2

Don't believe it's possible. RTL looks like focusing on validating against DOM not React's components tree.

The only workaround I see is to mock FetchNextPageButton to make it rendering all props into attributes.

jest.mock("../../../FetchNextPageButton.js", () => 
  (props) => <div data-test-id="FetchNextPageButton" {...props} />);
....
const { getByTestId } = render(<YourComponent />);
expect(getByTestId("FetchNextPageButton")).toHaveAttribute("query", NEWS_QUERY);
expect(getByTestId("FetchNextPageButton")).toHaveAttribute("path", "viewer.news");

Sure, this is smoothly only for primitive values in props, but validating something like object or function would be harder.

Think, it's not RTL-way, but I agree it would be massive work to check that in scope of each container(and completely ignoring that would be rather a risk).

PS toHaveAttribute is from jest-dom

Answer 3

In my case, I wanted to test that a Higher Order Component (HOC), correctly enhances the component that is passed to the HOC.

What I needed to do, is make the actual component a mock and pass it to the HOC. Like described in the existing answer, you can then just expect the properties, added by the HOC.

// after 'Component' get's passed into withSelectionConstraint, it should have an id prop
const Component = jest.fn(() => <h1>Tag Zam</h1>);
const WithConstraint = withSelectionConstraint(Component, ["instance"], true);
render(<WithConstraint />);

// passing the jest mock to the HOC, enables asserting the actual properties passed by the HOC
expect(Component).toHaveBeenCalledWith(
    expect.objectContaining({ ids: mockInstanceRows.map(x => x.id) }), 
    expect.anything()
)