Unit testing components

danger

Be careful when using jest.mock on modules like rest-hooks. Eliminating expected exports can lead to hard-to trace errors like TypeError: Class extends value undefined is not a function or null.

Instead either do a partial mock, or better mockResolvedValue on your endpoints.

If you need to add unit tests to your components to check some behavior you might want avoid dealing with network fetch cycle as that is probably orthogonal to what your are trying to test. Using <MockResolver /> in our tests allow us to prime the cache with provided fixtures so the components will immediately render with said results.

__tests__/fixtures.ts

export default {
  full: [
    {
      endpoint: ArticleResource.getList,
      args: [{ maxResults: 10 }] as const,
      response: [
        {
          id: 5,
          content: 'have a merry christmas',
          author: 2,
          contributors: [],
        },
        {
          id: 532,
          content: 'never again',
          author: 23,
          contributors: [5],
        },
      ],
    },
    {
      endpoint: ArticleResource.update(),
      args: [{ id: 532 }] as const,
      response: {
        id: 532,
        content: 'updated "never again"',
        author: 23,
        contributors: [5],
      },
    },
  ],
  empty: [
    {
      endpoint: ArticleResource.getList,
      args: [{ maxResults: 10 }] as const,
      response: [],
    },
  ],
  error: [
    {
      endpoint: ArticleResource.getList,
      args: [{ maxResults: 10 }] as const,
      response: { message: 'Bad request', status: 400, name: 'Not Found' },
      error: true,
    },
  ],
  loading: [],
};

__tests__/ArticleList.tsx

import { CacheProvider } from 'rest-hooks';
import { render } from '@testing-library/react';
import { MockResolver } from '@rest-hooks/test';

import ArticleList from 'components/ArticleList';
import results from './fixtures';

describe('<ArticleList />', () => {
  it('renders', () => {
    const tree = (
      <CacheProvider initialState={mockInitialState(results.full)}>
        <ArticleList maxResults={10} />
      </CacheProvider>
    );
    const { queryByText } = render(tree);
    const content = queryByText(results.full.result[0].content);
    expect(content).toBeDefined();
  });

  it('suspends then resolves', async () => {
    const tree = (
      <CacheProvider>
        <MockResolver fixtures={results.full}>
          <Suspense fallback="loading">
            <ArticleList maxResults={10} />
          </Suspense>
        </MockResolver>
      </CacheProvider>
    );
    const { queryByText, waitForNextUpdate } = render(tree);
    expect(queryByText('loading')).toBeDefined();

    await waitForNextUpdate();
    expect(queryByText(results.full.result[0].content)).toBeDefined();
  })
});