Testing

Testing with urql can be done in a multitude of ways. The most effective and straightforward method is to mock the Client to force your components into a fixed state during testing.

The following examples demonstrate this method of testing for React and the urql package only, however the pattern itself can be adapted for any framework-bindings of urql.

Mocking the client

For the most part, urql's hooks are just adapters for talking to the urql client.

The way in which they do this is by making calls to the client via context.

  • useQuery calls executeQuery
  • useMutation calls executeMutation
  • useSubscription calls executeSubscription

In the section "Stream Patterns" on the "Architecture" page we've seen, that all methods on the client operate with and return streams. These streams are created using the Wonka library, and we're able to create streams ourselves to mock the different states of our operations, e.g. fetching, errors, or success with data.

You'll probably use one of these utility functions to create streams:

  • never: This stream doesn’t emit any values and never completes, which puts our urql code in a permanent fetching: true state.
  • fromValue: This utility function accepts a value and emits it immediately, which we can use to mock a result from the server.
  • makeSubject: Allows us to create a source and imperatively push responses, which is useful to test subscription and simulate changes, i.e. multiple states.

Creating a mock Client is pretty quick as we'll create an object that contains the Client's methods that the React urql hooks use. We'll mock the appropriate execute functions that we need to mock a set of hooks. After we've created the mock Client we can wrap components with the Provider from urql and pass it.

Here's an example client mock being used while testing a component.

import { mount } from 'enzyme';
import { Provider } from 'urql';
import { never } from 'wonka';
import { MyComponent } from './MyComponent';
it('renders', () => {
const mockClient = {
executeQuery: jest.fn(() => never),
executeMutation: jest.fn(() => never),
executeSubscription: jest.fn(() => never),
};
const wrapper = mount(
<Provider value={mockClient}>
<MyComponent />
</Provider>
);
});

Testing calls to the client

Once you have your mock setup, calls to the client can be tested.

it('skips the query', () => {
mount(
<Provider value={mockClient}>
<MyComponent skip={true} />
</Provider>
);
expect(mockClient.executeQuery).toBeCalledTimes(0);
});

Testing mutations and subscriptions also work in a similar fashion.

it('triggers a mutation', () => {
const wrapper = mount(
<Provider value={mockClient}>
<MyComponent />
</Provider>
);
const variables = { name: 'Carla' };
wrapper.find('input').simulate('change', { currentTarget: { value: variables.name } });
wrapper.find('button').simulate('click');
expect(mockClient.executeMutation).toBeCalledTimes(1);
expect(mockClient.executeMutation).toBeCalledWith(expect.objectContaining({ variables }), {});
});

Forcing states

For testing render output, or creating fixtures, you may want to force the state of your components.

Fetching

Fetching states can be simulated by returning a stream, which never returns. Wonka provides a utility for this, aptly called never.

Here's a fixture, which stays in the fetching state.

import { Provider } from 'urql';
import { never } from 'wonka';
import { MyComponent } from './MyComponent';
const fetchingState = {
executeQuery: () => never,
};
export default (
<Provider value={fetchingState}>
<MyComponent />
</Provider>
);

Response (success)

Response states are simulated by providing a stream, which contains a network response. For single responses, Wonka's fromValue function can do this for us.

Example snapshot test of response state

it('matches snapshot', () => {
const responseState = {
executeQuery: () =>
fromValue({
data: {
posts: [
{ id: 1, title: 'Post title', content: 'This is a post' },
{ id: 3, title: 'Final post', content: 'Final post here' },
],
},
}),
};
const wrapper = mount(
<Provider value={responseState}>
<MyComponent />
</Provider>
);
expect(wrapper).toMatchSnapshot();
});

Response (error)

Error responses are similar to success responses, only the value in the stream is changed.

import { Provider, CombinedError } from 'urql';
const errorState = {
executeQuery: () =>
fromValue({
error: new CombinedError({
networkError: Error('something went wrong!'),
}),
}),
};

Handling multiple hooks

Returning different values for many useQuery calls can be done by introducing conditionals into the mocked client functions.

let mockClient;
beforeEach(() => {
mockClient = () => {
executeQuery: ({ query }) => {
if (query === GET_USERS) {
return fromValue(usersResponse);
}
if (query === GET_POSTS) {
return fromValue(postsResponse);
}
};
};
});

The above client we've created mocks all three operations — queries, mutations and subscriptions — to always remain in the fetching: true state. Generally when we're hoisting our mocked client and reuse it across multiple tests we have to be mindful not to instantiate the mocks outside of Jest's lifecycle functions (like it, beforeEach, beforeAll and such) as it may otherwise reset our mocked functions' return values or implementation.

Subscriptions

Testing subscriptions can be done by simulating the arrival of new data over time. To do this we may use the interval utility from Wonka, which emits values on a timer, and for each value we can map over the response that we'd like to mock.

If you prefer to have more control on when the new data is arriving you can use the makeSubject utility from Wonka. You can see more details in the next section.

Here's an example of testing a list component, which uses a subscription.

import { OperationContext, makeOperation } from '@urql/core';
it('should update the list', done => {
const mockClient = {
executeSubscription: jest.fn(query =>
pipe(
interval(200),
map((i: number) => ({
// To mock a full result, we need to pass a mock operation back as well
operation: makeOperation('subscription', query, {} as OperationContext),
data: { posts: { id: i, title: 'Post title', content: 'This is a post' } },
}))
)
),
};
let index = 0;
const wrapper = mount(
<Provider value={mockClient}>
<MyComponent />
</Provider>
);
setTimeout(() => {
expect(wrapper.find('.list').children()).toHaveLength(index + 1); // See how many items are in the list
index++;
if (index === 2) done();
}, 200);
});

Simulating changes

Simulating multiple responses can be useful, particularly testing useEffect calls dependent on changing query responses.

For this, a subject is the way to go. In short, it's a stream that you can push responses to. The makeSubject function from Wonka is what you'll want to use for this purpose.

Below is an example of simulating subsequent responses (such as a cache update/refetch) in a test.

import { mount } from 'enzyme';
import { act } from 'react-dom/test-utils';
import { Provider } from 'urql';
import { makeSubject } from 'wonka';
import { MyComponent } from './MyComponent';
const { source: stream, next: pushResponse } = makeSubject();
it('shows notification on updated data', () => {
const mockedClient = {
executeQuery: jest.fn(() => stream),
};
const wrapper = mount(
<Provider value={mockedClient}>
<MyComponent />
</Provider>
);
// First response
act(() => {
pushResponse({
data: {
posts: [{ id: 1, title: 'Post title', content: 'This is a post' }],
},
});
});
expect(wrapper.find('dialog').exists()).toBe(false);
// Second response
act(() => {
pushResponse({
data: {
posts: [
{ id: 1, title: 'Post title', content: 'This is a post' },
{ id: 1, title: 'Post title', content: 'This is a post' },
],
},
});
});
expect(wrapper.find('dialog').exists()).toBe(true);
});