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Testing guidelines

contribute/style-guides/testing.md

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Testing guidelines

The goal of this document is to address the most frequently asked "How to" questions related to unit testing.

  • Default to the *ByRole queries when testing components because it encourages testing with accessibility concerns in mind.
  • Alternatively, you could use *ByLabelText queries for testing components. However, we recommend the *ByRole queries because they are more robust.

Testing User Interactions

We use the user-event library for simulating user interactions during testing. This library is preferred over the built-in fireEvent method, as it more accurately mirrors real user interactions with elements.

There are two important considerations when working with userEvent:

  1. All methods in userEvent are asynchronous, and thus require the use of await when called.
  2. Directly calling methods from userEvent may not be supported in future versions. As such, it's necessary to first call userEvent.setup() prior to the tests. This method returns a userEvent instance, complete with all its methods. This setup process can be simplified using a utility function:
tsx
import { render, screen } from '@testing-library/react';
import userEvent from '@testing-library/user-event';

function setup(jsx: JSX.Element) {
  return {
    user: userEvent.setup(),
    ...render(jsx),
  };
}

it('should render', async () => {
  const { user } = setup(<Button />);
  await user.click(screen.getByRole('button'));
});

Debug tests

There are a few utilities that can be useful for debugging tests:

  • screen.debug() - This function prints a human-readable representation of the document's DOM tree when called without arguments, or the DOM tree of specific node or nodes when provided with arguments. It is internally using console.log to log the output to terminal.
  • Testing Playground - An interactive sandbox that allows testing of which queries work with specific HTML elements.
  • prettyDOM logRoles - A utility function that prints out all the implicit ARIA roles for a given DOM tree.

Testing select components

Here, the OrgRolePicker component is used as an example. This component essentially serves as a wrapper for the Select component, complete with its own set of options.

tsx
import { OrgRole } from '@grafana/data';
import { Select } from '@grafana/ui';

interface Props {
  value: OrgRole;
  disabled?: boolean;
  'aria-label'?: string;
  inputId?: string;
  onChange: (role: OrgRole) => void;
  autoFocus?: boolean;
  width?: number | 'auto';
}

const options = Object.keys(OrgRole).map((key) => ({ label: key, value: key }));

export function OrgRolePicker({ value, onChange, 'aria-label': ariaLabel, inputId, autoFocus, ...restProps }: Props) {
  return (
    <Select
      inputId={inputId}
      value={value}
      options={options}
      onChange={(val) => onChange(val.value as OrgRole)}
      placeholder="Choose role..."
      aria-label={ariaLabel}
      autoFocus={autoFocus}
      {...restProps}
    />
  );
}

Querying the Select Component

It is a recommended practice to query Select components by using a label. Add a label element and provide the htmlFor prop with a matching inputId. Alternatively, you can specify aria-label on the Select statement.

tsx
describe('OrgRolePicker', () => {
  it('should render the picker', () => {
    setup(
      <>
        <label htmlFor={'role-picker'}>Role picker</label>
        <OrgRolePicker value={OrgRole.Admin} inputId={'role-picker'} onChange={() => {}} />
      </>
    );
    expect(screen.getByRole('combobox', { name: 'Role picker' })).toBeInTheDocument();
  });
});

Test the display of correct options

At times, it might be necessary to verify that the Select component is displaying the correct options. In such instances, the best solution is to click the Select component and match the desired option using the *ByText query.

tsx
it('should have an "Editor" option', async () => {
  const { user } = setup(
    <>
      <label htmlFor={'role-picker'}>Role picker</label>
      <OrgRolePicker value={OrgRole.Admin} inputId={'role-picker'} onChange={() => {}} />
    </>
  );
  await user.click(screen.getByRole('combobox', { name: 'Role picker' }));
  expect(screen.getByText('Editor')).toBeInTheDocument();
});

Selecting an option

To simplify the process of selecting an option from a Select component, there is a selectOptionInTest utility function. This function is a wrapper over the react-select-event package.

tsx
it('should select an option', async () => {
  const mockOnChange = jest.fn();
  setup(
    <>
      <label htmlFor={'role-picker'}>Role picker</label>
      <OrgRolePicker value={OrgRole.Admin} inputId={'role-picker'} onChange={mockOnChange} />
    </>
  );
  await selectOptionInTest(screen.getByRole('combobox', { name: 'Role picker' }), 'Viewer');
  expect(mockOnChange).toHaveBeenCalledWith('Viewer');
});

Mock objects and functions

Mock the window object and its methods

The recommended approach for mocking the window object is to use Jest spies. Jest's spy functions provide a built-in mechanism for restoring mocks. This feature eliminates the need to manually save a reference to the window object.

tsx
let windowSpy: jest.SpyInstance;

beforeAll(() => {
  windowSpy = jest.spyOn(window, 'location', 'get');
});

afterAll(() => {
  windowSpy.mockRestore();
});

it('should test with window', function () {
  windowSpy.mockImplementation(() => ({
    href: 'www.example.com',
  }));
  expect(window.location.href).toBe('www.example.com');
});

Mocking getBackendSrv()

Use the getBackendSrv() function to make HTTP requests to the Grafana backend. It is possible to mock this function using the jest.mock method.

tsx
jest.mock('@grafana/runtime', () => ({
  ...jest.requireActual('@grafana/runtime'),
  getBackendSrv: () => ({
    post: postMock,
  }),
}));

Mocking getBackendSrv for AsyncSelect

Use the AsyncSelect component to asynchronously load options. This component often relies on the getBackendSrv for loading the options.

Here's what the test looks like for this OrgPicker component, which uses AsyncSelect under the hood:

tsx
import { screen, render } from '@testing-library/react';
import userEvent from '@testing-library/user-event';

import { OrgPicker } from './OrgPicker';

jest.mock('@grafana/runtime', () => ({
  ...jest.requireActual('@grafana/runtime'),
  getBackendSrv: () => ({
    get: () =>
      Promise.resolve([
        { name: 'Org 1', id: 0 },
        { name: 'Org 2', id: 1 },
      ]),
  }),
}));

function setup(jsx: JSX.Element) {
  return {
    user: userEvent.setup(),
    ...render(jsx),
  };
}

describe('OrgPicker', () => {
  it('should render', async () => {
    render(
      <>
        <label htmlFor={'picker'}>Org picker</label>
        <OrgPicker onSelected={() => {}} inputId={'picker'} />
      </>
    );

    expect(await screen.findByRole('combobox', { name: 'Org picker' })).toBeInTheDocument();
  });

  it('should have the options', async () => {
    const { user } = setup(
      <>
        <label htmlFor={'picker'}>Org picker</label>
        <OrgPicker onSelected={() => {}} inputId={'picker'} />
      </>
    );
    await user.click(await screen.findByRole('combobox', { name: 'Org picker' }));
    expect(screen.getByText('Org 1')).toBeInTheDocument();
    expect(screen.getByText('Org 2')).toBeInTheDocument();
  });
});