jest.js

module.exports = {
	// Let ESLint know we are using the common Jest environment and its globals
	"env": {
		"jest": true,
		"jest/globals": true,
	},

	// Include jest and node plugin
	"plugins": [
		"node",
		"jest",
	],

	// Extend sharable configs from jest
	"extends": [
		"plugin:jest/recommended",
		// Reason: Style of tests, assertions and better error messages
		"plugin:jest/style",
	],

	"rules": {
		// Reason: Some matcher aliases are easier to understand (grammar)
		"jest/no-alias-methods": "off",
		// Reason: Ensures the correct error was thrown and not a logic or testing error
		"jest/require-to-throw-message": "error",
		// Reason: Possible error or confusing format of test hooks
		"jest/no-duplicate-hooks": "error",
		// Reason: Avoid loosing hooks in the middle of tests when they will apply to ones above and below
		"jest/prefer-hooks-on-top": "error",
		// Reason: Avoid writing extremely loose tests like `expect(value).toBeTruthy()`
		"jest/no-restricted-matchers": [
			"error",
			{
				"toBeFalsy": "Use a more restrictive expectation e.g. `.toBe(false)`, `.toBeNull()`, `.not.toBeInTheDocument()`",
				"toBeTruthy": "Use a more restrictive expectation e.g. `.toBe(true)`, `.toEqual(value)`, `.toBeInTheDocument()`",
			},
		],
	},

	"overrides": [
		{
			// Apply to TypeScript files
			"files": [
				"**/*.{ts,tsx}",
			],
			"rules": {
				// Reason: Replace unbound method lint rules in TypeScript to automatically allow certain
				// unbound methods that are safe in tests
				"@typescript-eslint/unbound-method": "off",
				"jest/unbound-method": "error",
			},
		},
	],
};