feat: create require-hook rule (#929)

README.md

@@ -189,6 +189,7 @@ installations requiring long-term consistency.
 | [prefer-to-contain](docs/rules/prefer-to-contain.md)                         | Suggest using `toContain()`                                         | ![style][]       | ![fixable][] |
 | [prefer-to-have-length](docs/rules/prefer-to-have-length.md)                 | Suggest using `toHaveLength()`                                      | ![style][]       | ![fixable][] |
 | [prefer-todo](docs/rules/prefer-todo.md)                                     | Suggest using `test.todo`                                           |                  | ![fixable][] |
+| [require-hook](docs/rules/require-hook.md)                                   | Require setup and teardown code to be within a hook                 |                  |              |
 | [require-to-throw-message](docs/rules/require-to-throw-message.md)           | Require a message for `toThrow()`                                   |                  |              |
 | [require-top-level-describe](docs/rules/require-top-level-describe.md)       | Require test cases and hooks to be inside a `describe` block        |                  |              |
 | [valid-describe](docs/rules/valid-describe.md)                               | Enforce valid `describe()` callback                                 | ![recommended][] |              |

docs/rules/require-hook.md

@@ -0,0 +1,149 @@
+# Require setup and teardown code to be within a hook (`require-hook`)
+
+Often while writing tests you have some setup work that needs to happen before
+tests run, and you have some finishing work that needs to happen after tests
+run. Jest provides helper functions to handle this.
+
+It's common when writing tests to need to perform setup work that needs 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_
+- 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:
+
+```js
+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:
+
+```js
+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();
+});
+```

src/__tests__/__snapshots__/rules.test.ts.snap

@@ -47,6 +47,7 @@ Object {
       "jest/prefer-to-contain": "error",
       "jest/prefer-to-have-length": "error",
       "jest/prefer-todo": "error",
+      "jest/require-hook": "error",
       "jest/require-to-throw-message": "error",
       "jest/require-top-level-describe": "error",
       "jest/unbound-method": "error",

src/__tests__/rules.test.ts

@@ -2,7 +2,7 @@ import { existsSync } from 'fs';
 import { resolve } from 'path';
 import plugin from '../';
 
-const numberOfRules = 48;
+const numberOfRules = 49;
 const ruleNames = Object.keys(plugin.rules);
 const deprecatedRules = Object.entries(plugin.rules)
   .filter(([, rule]) => rule.meta.deprecated)