require-hook.md

Require setup and teardown code to be within a hook (require-hook)

It's common when writing tests to need to perform setup work that has to happen before tests run, and finishing work after tests run.

Because Jest executes all describe handlers in a test file before it executes any of the actual tests, it's important to ensure setup and teardown work is done inside before* and after* handlers respectively, rather than inside the describe blocks.

Rule details

This rule flags any expression that is either at the toplevel of a test file or directly within the body of a describe, except for the following:

• import statements
• const variables
• let declarations, and initializations to null or undefined
• Classes
• Types
• Calls to the standard Jest globals

This rule flags any function calls within test files that are directly within the body of a describe, and suggests wrapping them in one of the four lifecycle hooks.

Here is a slightly contrived test file showcasing some common cases that would be flagged:

import { database, isCity } from '../database';
import { Logger } from '../../../src/Logger';
import { loadCities } from '../api';

jest.mock('../api');

const initializeCityDatabase = () => {
  database.addCity('Vienna');
  database.addCity('San Juan');
  database.addCity('Wellington');
};

const clearCityDatabase = () => {
  database.clear();
};

initializeCityDatabase();

test('that persists cities', () => {
  expect(database.cities.length).toHaveLength(3);
});

test('city database has Vienna', () => {
  expect(isCity('Vienna')).toBeTruthy();
});

test('city database has San Juan', () => {
  expect(isCity('San Juan')).toBeTruthy();
});

describe('when loading cities from the api', () => {
  let consoleWarnSpy = jest.spyOn(console, 'warn');

  loadCities.mockResolvedValue(['Wellington', 'London']);

  it('does not duplicate cities', async () => {
    await database.loadCities();

    expect(database.cities).toHaveLength(4);
  });

  it('logs any duplicates', async () => {
    await database.loadCities();

    expect(consoleWarnSpy).toHaveBeenCalledWith(
      'Ignored duplicate cities: Wellington',
    );
  });
});

clearCityDatabase();

Here is the same slightly contrived test file showcasing the same common cases but in ways that would be not flagged:

import { database, isCity } from '../database';
import { Logger } from '../../../src/Logger';
import { loadCities } from '../api';

jest.mock('../api');

const initializeCityDatabase = () => {
  database.addCity('Vienna');
  database.addCity('San Juan');
  database.addCity('Wellington');
};

const clearCityDatabase = () => {
  database.clear();
};

beforeEach(() => {
  initializeCityDatabase();
});

test('that persists cities', () => {
  expect(database.cities.length).toHaveLength(3);
});

test('city database has Vienna', () => {
  expect(isCity('Vienna')).toBeTruthy();
});

test('city database has San Juan', () => {
  expect(isCity('San Juan')).toBeTruthy();
});

describe('when loading cities from the api', () => {
  let consoleWarnSpy;

  beforeEach(() => {
    consoleWarnSpy = jest.spyOn(console, 'warn');
    loadCities.mockResolvedValue(['Wellington', 'London']);
  });

  it('does not duplicate cities', async () => {
    await database.loadCities();

    expect(database.cities).toHaveLength(4);
  });

  it('logs any duplicates', async () => {
    await database.loadCities();

    expect(consoleWarnSpy).toHaveBeenCalledWith(
      'Ignored duplicate cities: Wellington',
    );
  });
});

afterEach(() => {
  clearCityDatabase();
});

Options

If there are methods that you want to call outside of hooks and tests, you can mark them as allowed using the allowedFunctionCalls option.

{
  "jest/require-hook": [
    "error",
    {
      "allowedFunctionCalls": ["enableAutoDestroy"]
    }
  ]
}

Examples of correct code when using { "allowedFunctionCalls": ["enableAutoDestroy"] } option:

/* eslint jest/require-hook: ["error", { "allowedFunctionCalls": ["enableAutoDestroy"] }] */

import { enableAutoDestroy, mount } from '@vue/test-utils';
import { initDatabase, tearDownDatabase } from './databaseUtils';

enableAutoDestroy(afterEach);

beforeEach(initDatabase);
afterEach(tearDownDatabase);

describe('Foo', () => {
  test('always returns 42', () => {
    expect(global.getAnswer()).toBe(42);
  });
});