Component Testing with Cypress and Reactjs

Cypress has a feature called Component Testing, and I found the experience using it quite interesting, and familiar for those coming from non-UI testing suites. I assume that you have basic knowledge of Reactjs and Cypress and perhaps React Testing Library and Jest so I will skip the details and focus on the core concept.

Let us assume we have created a Parent component that renders a Child component. Parent makes an API request to a backend, stores it in state, and renders it to Child via props. We are adding some tests to make sure that the Child properly renders the data, and nothing crashes if some part of the data is missing. Simple stuff, typical example.

For our testing purposes we don't need a proper backend API to make our request since we're going to stub it. We can write something like:

export async function getData() {
  const {data} = await axios.get('/api/users/');
  return data
}

...and then we call getData in our useEffect, store the user object in state, pass the user as a prop to our child component, blah blah, you know the part. Now let's get down to business!

We start writing our mock data:

const MOCK_DATA = {
    user: {
      address: '33265 Kirlin Center',
      name: 'Enoch',
      lastName: 'Graham',
      city: 'Port Neha',
      country: 'Berkshire',
    },
};

Since Parent is making the request, we need to use the intercept command to stub the response.

describe('<Parent/>', () => {
  it('renders', () => {
    cy.intercept('GET', '/api/users/', (req) => {
      req.reply({
        statusCode: 200,
        body: MOCK_DATA, // <---
      });
    });

    cy.mount(<Parent />);
  });
});

We are now ready to add more assertions by modifying the MOCK_DATA object, for example to test what happens when address is undefined.

With the React Testing Library and Jest, we would do pretty much the same thing: We would use something like jest.spyOn in combination with mockResolvedValue to intercept the request and mock the response.

What is great about Cypress Component Testing is that we have a visual representation of our test with simple methods, which is a big enhacement in terms of the development experience.

Some notes on configuring Cypress, and improving your testing strategy:

• When Cypress creates a component test, you will notice that the styles are not applied. Simply follow the relevant documentation to solve this.
• If you are using Typescript, you will probably need to configure tsconfig.json so that Cypress types are recognized.
• Use faker.js and factories to generate random values for your mock data.

Cheers!