[tests] migrate from jest to vitest (#3940)

This is a big change, but I think it's a good move, as `vitest` is much
more modern than `jest`.

I'm excited about the UI watch feature (run `npm run test:ui`), for
example - it's really helpful and saves time when debugging tests. I had
to adjust a few tests because they had time related issues, but
basically we are now testing the same things - even a bit better and
less flaky (I hope).

What do you think?

Author: KristjanESPERANTO

.github/CONTRIBUTING.md

@@ -30,9 +30,19 @@ To run markdownlint, use `node --run lint:markdown`.
 
 ## Testing
 
-We use [Jest](https://jestjs.io) for JavaScript testing.
+We use [Vitest](https://vitest.dev) for JavaScript testing.
 
 To run all tests, use `node --run test`.
 
-The specific test commands are defined in `package.json`.
-So you can also run the specific tests with other commands, e.g. `node --run test:unit` or `npx jest tests/e2e/env_spec.js`.
+The `package.json` scripts expose finer-grained test commands:
+
+- `test:unit` – run unit tests only
+- `test:e2e` – execute browser-driven end-to-end tests
+- `test:electron` – launch the Electron-based regression suite
+- `test:coverage` – collect coverage while running every suite
+- `test:watch` – keep Vitest in watch mode for fast local feedback
+- `test:ui` – open the Vitest UI dashboard (needs OS file-watch support enabled)
+- `test:calendar` – run the legacy calendar debug helper
+- `test:css`, `test:markdown`, `test:prettier`, `test:spelling`, `test:js` – lint-only scripts that enforce formatting, spelling, markdown style, and ESLint.
+
+You can invoke any script with `node --run <script>` (or `npm run <script>`). Individual files can still be targeted directly, e.g. `npx vitest run tests/e2e/env_spec.js`.

.gitignore

@@ -88,3 +88,6 @@ js/positions.js
 # Ignore lock files other than package-lock.json
 pnpm-lock.yaml
 yarn.lock
+
+# Vitest temporary test files
+tests/**/.tmp/

CHANGELOG.md

@@ -22,6 +22,7 @@ planned for 2026-01-01
 - [check_config] refactor: improve error handling (#3927)
 - [calendar] test: remove "Recurring event per timezone" test (#3929)
 - [calendar] chore: remove `requiresVersion: "2.1.0"` (#3932)
+- [tests] migrate from `jest` to `vitest` (#3940)
 
 ### Fixed
 

eslint.config.mjs

@@ -1,11 +1,11 @@
 import {defineConfig, globalIgnores} from "eslint/config";
 import globals from "globals";
 import {flatConfigs as importX} from "eslint-plugin-import-x";
-import jest from "eslint-plugin-jest";
 import js from "@eslint/js";
 import jsdocPlugin from "eslint-plugin-jsdoc";
 import packageJson from "eslint-plugin-package-json";
 import stylistic from "@stylistic/eslint-plugin";
+import vitest from "eslint-plugin-vitest";
 
 export default defineConfig([
 	globalIgnores(["config/**", "modules/**/*", "!modules/default/**", "js/positions.js"]),
@@ -16,15 +16,16 @@ export default defineConfig([
 			globals: {
 				...globals.browser,
 				...globals.node,
+				...vitest.environments.env.globals,
 				Log: "readonly",
 				MM: "readonly",
 				Module: "readonly",
 				config: "readonly",
 				moment: "readonly"
 			}
 		},
-		plugins: {js, stylistic},
-		extends: [importX.recommended, jest.configs["flat/recommended"], "js/recommended", jsdocPlugin.configs["flat/recommended"], "stylistic/all"],
+		plugins: {js, stylistic, vitest},
+		extends: [importX.recommended, vitest.configs.recommended, "js/recommended", jsdocPlugin.configs["flat/recommended"], "stylistic/all"],
 		rules: {
 			"@stylistic/array-element-newline": ["error", "consistent"],
 			"@stylistic/arrow-parens": ["error", "always"],
@@ -57,12 +58,9 @@ export default defineConfig([
 			"import-x/newline-after-import": "error",
 			"import-x/order": "error",
 			"init-declarations": "off",
-			"jest/consistent-test-it": "warn",
-			"jest/no-done-callback": "warn",
-			"jest/prefer-expect-resolves": "warn",
-			"jest/prefer-mock-promise-shorthand": "warn",
-			"jest/prefer-to-be": "warn",
-			"jest/prefer-to-have-length": "warn",
+			"vitest/consistent-test-it": "warn",
+			"vitest/prefer-to-be": "warn",
+			"vitest/prefer-to-have-length": "warn",
 			"max-lines-per-function": ["warn", 400],
 			"max-statements": "off",
 			"no-global-assign": "off",

js/app.js

@@ -65,8 +65,8 @@ function App () {
 	async function loadConfig () {
 		Log.log("Loading config ...");
 		const defaults = require(`${__dirname}/defaults`);
-		if (process.env.JEST_WORKER_ID !== undefined) {
-			// if we are running with jest
+		if (global.mmTestMode) {
+			// if we are running in test mode
 			defaults.address = "0.0.0.0";
 		}
 
@@ -185,10 +185,10 @@ function App () {
 
 		if (defaultModules.includes(moduleName)) {
 			const defaultModuleFolder = path.resolve(`${global.root_path}/modules/default/`, module);
-			if (process.env.JEST_WORKER_ID === undefined) {
+			if (!global.mmTestMode) {
 				moduleFolder = defaultModuleFolder;
 			} else {
-				// running in Jest, allow defaultModules placed under moduleDir for testing
+				// running in test mode, allow defaultModules placed under moduleDir for testing
 				if (env.modulesDir === "modules" || env.modulesDir === "tests/mocks") {
 					moduleFolder = defaultModuleFolder;
 				}

js/electron.js

@@ -76,8 +76,8 @@ function createWindow () {
 
 	const electronOptions = Object.assign({}, electronOptionsDefaults, config.electronOptions);
 
-	if (process.env.JEST_WORKER_ID !== undefined && process.env.MOCK_DATE !== undefined) {
-		// if we are running with jest and we want to mock the current date
+	if (process.env.MOCK_DATE !== undefined) {
+		// if we are running tests and we want to mock the current date
 		const fakeNow = new Date(process.env.MOCK_DATE).valueOf();
 		Date = class extends Date {
 			constructor (...args) {
@@ -114,8 +114,8 @@ function createWindow () {
 
 	// Open the DevTools if run with "node --run start:dev"
 	if (process.argv.includes("dev")) {
-		if (process.env.JEST_WORKER_ID !== undefined) {
-			// if we are running with jest
+		if (process.env.mmTestMode) {
+			// if we are running tests
 			const devtools = new BrowserWindow(electronOptions);
 			mainWindow.webContents.setDevToolsWebContents(devtools.webContents);
 		}
@@ -169,8 +169,8 @@ function createWindow () {
 
 // Quit when all windows are closed.
 app.on("window-all-closed", function () {
-	if (process.env.JEST_WORKER_ID !== undefined) {
-		// if we are running with jest
+	if (process.env.mmTestMode) {
+		// if we are running tests
 		app.quit();
 	} else {
 		createWindow();

js/loader.js

@@ -84,7 +84,7 @@ const Loader = (function () {
 				if (window.name !== "jsdom") {
 					moduleFolder = defaultModuleFolder;
 				} else {
-					// running in Jest, allow defaultModules placed under moduleDir for testing
+					// running in test mode, allow defaultModules placed under moduleDir for testing
 					if (envVars.modulesDir === "modules") {
 						moduleFolder = defaultModuleFolder;
 					}

js/logger.js

@@ -1,7 +1,7 @@
 // This logger is very simple, but needs to be extended.
 (function (root, factory) {
 	if (typeof exports === "object") {
-		if (process.env.JEST_WORKER_ID === undefined) {
+		if (process.env.mmTestMode !== "true") {
 			const { styleText } = require("node:util");
 
 			// add timestamps in front of log messages
@@ -78,8 +78,8 @@
 	let logLevel;
 	let enableLog;
 	if (typeof exports === "object") {
-		// in nodejs and not running with jest
-		enableLog = process.env.JEST_WORKER_ID === undefined;
+		// in nodejs and not running in test mode
+		enableLog = process.env.mmTestMode !== "true";
 	} else {
 		// in browser and not running with jsdom
 		enableLog = typeof window === "object" && window.name !== "jsdom";
@@ -97,7 +97,7 @@
 			groupEnd: Function.prototype.bind.call(console.groupEnd, console),
 			time: Function.prototype.bind.call(console.time, console),
 			timeEnd: Function.prototype.bind.call(console.timeEnd, console),
-			timeStamp: Function.prototype.bind.call(console.timeStamp, console)
+			timeStamp: console.timeStamp ? Function.prototype.bind.call(console.timeStamp, console) : function () {}
 		};
 
 		logLevel.setLogLevel = function (newLevel) {

js/module_functions.js

@@ -5,8 +5,8 @@
  * @param {Promise} callback function to call when the timer expires
  */
 const scheduleTimer = function (timer, intervalMS, callback) {
-	if (process.env.JEST_WORKER_ID === undefined) {
-		// only set timer when not running in jest
+	if (process.env.mmTestMode !== "true") {
+		// only set timer when not running in test mode
 		let tmr = timer;
 		clearTimeout(tmr);
 		tmr = setTimeout(function () {

js/utils.js

@@ -34,7 +34,7 @@ module.exports = {
 			].join("\n");
 			Log.info(systemDataString);
 
-			// Return is currently only for jest
+			// Return is currently only for tests
 			return systemDataString;
 		} catch (error) {
 			Log.error(error);
@@ -65,8 +65,10 @@ module.exports = {
 				if (results && results.length > 0) {
 					// get the position parts and replace space with underscore
 					const positionName = results[1].replace(" ", "_");
-					// add it to the list
-					modulePositions.push(positionName);
+					// add it to the list only if not already present (avoid duplicates)
+					if (!modulePositions.includes(positionName)) {
+						modulePositions.push(positionName);
+					}
 				}
 			});
 			try {