jest/require-hook Style

What it does

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

Example

// invalid
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);
  });
});
clearCityDatabase();

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

References

• Rule Source