feat: add harness-based jest runner

apps/playground/jest.config.js

@@ -0,0 +1,10 @@
+module.exports = {
+  projects: [
+    {
+      runner: '@react-native-harness/jest',
+      testMatch: [
+        '<rootDir>/src/__tests__/**/*.(test|spec|harness).(js|jsx|ts|tsx)',
+      ],
+    },
+  ],
+};

apps/playground/package.json

@@ -5,5 +5,9 @@
   "dependencies": {
     "react-native": "*",
     "react-native-harness": "workspace:*"
+  },
+  "devDependencies": {
+    "@react-native-harness/jest": "workspace:*",
+    "jest": "^30.2.0"
   }
 }

apps/playground/tsconfig.app.json

@@ -33,6 +33,9 @@
     "react-native-harness.d.ts"
   ],
   "references": [
+    {
+      "path": "../../packages/jest/tsconfig.lib.json"
+    },
     {
       "path": "../../packages/react-native-harness/tsconfig.lib.json"
     }

apps/playground/tsconfig.json

@@ -3,6 +3,9 @@
   "files": [],
   "include": [],
   "references": [
+    {
+      "path": "../../packages/jest"
+    },
     {
       "path": "../../packages/react-native-harness"
     },

packages/cli/package.json

@@ -5,6 +5,21 @@
   "main": "./dist/index.js",
   "module": "./dist/index.js",
   "types": "./dist/index.d.ts",
+  "exports": {
+    "./package.json": "./package.json",
+    ".": {
+      "development": "./src/index.ts",
+      "types": "./dist/index.d.ts",
+      "import": "./dist/index.js",
+      "default": "./dist/index.js"
+    },
+    "./external": {
+      "development": "./src/external.ts",
+      "types": "./dist/external.d.ts",
+      "import": "./dist/external.js",
+      "default": "./dist/external.js"
+    }
+  },
   "dependencies": {
     "@react-native-harness/bridge": "workspace:*",
     "@react-native-harness/config": "workspace:*",

packages/cli/src/external.ts

@@ -0,0 +1,44 @@
+import { TestRunnerConfig } from '@react-native-harness/config';
+import { Environment } from './platforms/platform-adapter.js';
+import {
+  BridgeServer,
+  getBridgeServer,
+} from '@react-native-harness/bridge/server';
+import { BridgeTimeoutError } from './errors/errors.js';
+import { getPlatformAdapter } from './platforms/platform-registry.js';
+
+export type Harness = {
+  environment: Environment;
+  bridge: BridgeServer;
+};
+
+export const getHarness = async (
+  runner: TestRunnerConfig
+): Promise<Harness> => {
+  const bridgeTimeout = 60000;
+  const platformAdapter = await getPlatformAdapter(runner.platform);
+  const serverBridge = await getBridgeServer({
+    port: 3001,
+  });
+
+  const readyPromise = new Promise<void>((resolve, reject) => {
+    const timeout = setTimeout(() => {
+      reject(
+        new BridgeTimeoutError(bridgeTimeout, runner.name, runner.platform)
+      );
+    }, bridgeTimeout);
+
+    serverBridge.once('ready', () => {
+      clearTimeout(timeout);
+      resolve();
+    });
+  });
+
+  const environment = await platformAdapter.getEnvironment(runner);
+  await readyPromise;
+
+  return {
+    environment,
+    bridge: serverBridge,
+  };
+};

packages/jest/README.md

@@ -0,0 +1,40 @@
+![harness-banner](https://react-native-harness.dev/harness-banner.jpg)
+
+### Experimental Jest Runner for React Native Harness
+
+[![mit licence][license-badge]][license]
+[![npm downloads][npm-downloads-badge]][npm-downloads]
+[![Chat][chat-badge]][chat]
+[![PRs Welcome][prs-welcome-badge]][prs-welcome]
+
+⚠️ **EXPERIMENTAL** ⚠️
+
+An experimental Jest runner that integrates React Native Harness with Jest's infrastructure. This package allows you to leverage existing Jest features like watchers, coverage reporting, and the familiar developer experience while running React Native Harness tests.
+
+## Features
+
+- **Jest Integration**: Re-uses Jest's existing infrastructure for a familiar developer experience
+- **Watch Mode**: Automatic test re-running when files change
+- **Coverage Reports**: Built-in code coverage support through Jest
+- **Serial Execution**: Tests run sequentially to ensure proper React Native environment management
+- **Harness Configuration**: Supports all React Native Harness runners and configurations
+
+## Usage
+
+This runner is designed to work with Jest's test runner system. Configure it in your Jest configuration to run React Native Harness tests through Jest's interface.
+
+## Made with ❤️ at Callstack
+
+`@react-native-harness/jest` is an open source project and will always remain free to use. If you think it's cool, please star it 🌟. [Callstack][callstack-readme-with-love] is a group of React and React Native geeks, contact us at [hello@callstack.com](mailto:hello@callstack.com) if you need any help with these or just want to say hi!
+
+Like the project? ⚛️ [Join the team](https://callstack.com/careers/?utm_campaign=Senior_RN&utm_source=github&utm_medium=readme) who does amazing stuff for clients and drives React Native Open Source! 🔥
+
+[callstack-readme-with-love]: https://callstack.com/?utm_source=github.com&utm_medium=referral&utm_campaign=react-native-harness&utm_term=readme-with-love
+[license-badge]: https://img.shields.io/npm/l/@react-native-harness/jest?style=for-the-badge
+[license]: https://github.com/callstackincubator/react-native-harness/blob/main/LICENSE
+[npm-downloads-badge]: https://img.shields.io/npm/dm/@react-native-harness/jest?style=for-the-badge
+[npm-downloads]: https://www.npmjs.com/package/@react-native-harness/jest
+[prs-welcome-badge]: https://img.shields.io/badge/PRs-welcome-brightgreen.svg?style=for-the-badge
+[prs-welcome]: ../../CONTRIBUTING.md
+[chat-badge]: https://img.shields.io/discord/426714625279524876.svg?style=for-the-badge
+[chat]: https://discord.gg/xgGt7KAjxv

packages/jest/eslint.config.mjs

@@ -0,0 +1,19 @@
+import baseConfig from '../../eslint.config.mjs';
+
+export default [
+  ...baseConfig,
+  {
+    files: ['**/*.json'],
+    rules: {
+      '@nx/dependency-checks': [
+        'error',
+        {
+          ignoredFiles: ['{projectRoot}/eslint.config.{js,cjs,mjs,ts,cts,mts}'],
+        },
+      ],
+    },
+    languageOptions: {
+      parser: await import('jsonc-eslint-parser'),
+    },
+  },
+];

packages/jest/package.json

@@ -0,0 +1,30 @@
+{
+  "name": "@react-native-harness/jest",
+  "version": "1.0.0-alpha.15",
+  "type": "module",
+  "main": "./dist/index.js",
+  "module": "./dist/index.js",
+  "types": "./dist/index.d.ts",
+  "exports": {
+    "./package.json": "./package.json",
+    ".": {
+      "development": "./src/index.ts",
+      "types": "./dist/index.d.ts",
+      "import": "./dist/index.js",
+      "default": "./dist/index.js"
+    }
+  },
+  "dependencies": {
+    "@jest/test-result": "^30.2.0",
+    "jest-runner": "^30.2.0",
+    "p-limit": "^7.1.1",
+    "tslib": "^2.3.0",
+    "yargs": "^17.7.2",
+    "@react-native-harness/cli": "workspace:*",
+    "@react-native-harness/bridge": "workspace:*",
+    "@react-native-harness/config": "workspace:*"
+  },
+  "devDependencies": {
+    "@types/yargs": "^17.0.32"
+  }
+}

packages/jest/src/cli-args.ts

@@ -0,0 +1,29 @@
+import yargs from 'yargs';
+import { hideBin } from 'yargs/helpers';
+
+export type HarnessCliArgs = {
+  harnessRunner?: string;
+};
+
+export const getAdditionalCliArgs = (): HarnessCliArgs => {
+  const argv = yargs(hideBin(process.argv))
+    .option('harnessRunner', {
+      type: 'string',
+      description: 'Specify which Harness runner to use',
+      coerce: (value: string) => {
+        if (!value || value.trim().length === 0) {
+          throw new Error('harnessRunner must be a non-empty string');
+        }
+        return value.trim();
+      },
+    })
+    .strict(false)
+    .help(false)
+    .version(false)
+    .exitProcess(false)
+    .parseSync();
+
+  return {
+    harnessRunner: argv.harnessRunner,
+  };
+};

packages/jest/src/index.ts

@@ -0,0 +1,129 @@
+import type {
+  CallbackTestRunnerInterface,
+  Config,
+  OnTestFailure,
+  OnTestStart,
+  OnTestSuccess,
+  Test,
+  TestRunnerOptions,
+  TestWatcher,
+} from 'jest-runner';
+import pLimit from 'p-limit';
+import { runHarnessTestFile } from './run.js';
+import { getHarness } from '@react-native-harness/cli/external';
+import {
+  getConfig,
+  Config as HarnessConfig,
+  TestRunnerConfig as HarnessTestRunnerConfig,
+} from '@react-native-harness/config';
+import { getAdditionalCliArgs, HarnessCliArgs } from './cli-args.js';
+import type { Harness } from '@react-native-harness/cli/external';
+
+class CancelRun extends Error {
+  constructor(message?: string) {
+    super(message);
+    this.name = 'CancelRun';
+  }
+}
+
+const getHarnessRunner = (
+  config: HarnessConfig,
+  cliArgs: HarnessCliArgs
+): HarnessTestRunnerConfig => {
+  const selectedRunnerName = cliArgs.harnessRunner ?? config.defaultRunner;
+  const runner = config.runners.find(
+    (runner) => runner.name === selectedRunnerName
+  );
+
+  if (!runner) {
+    throw new Error(`Runner "${selectedRunnerName}" not found`);
+  }
+
+  return runner;
+};
+export default class JestHarness implements CallbackTestRunnerInterface {
+  readonly isSerial = true;
+
+  #globalConfig: Config.GlobalConfig;
+
+  constructor(globalConfig: Config.GlobalConfig) {
+    this.#globalConfig = globalConfig;
+  }
+
+  async runTests(
+    tests: Array<Test>,
+    watcher: TestWatcher,
+    onStart: OnTestStart,
+    onResult: OnTestSuccess,
+    onFailure: OnTestFailure,
+    options: TestRunnerOptions
+  ): Promise<void> {
+    if (!options.serial) {
+      throw new Error('Parallel test running is not supported');
+    }
+
+    const projectRoot = this.#globalConfig.rootDir;
+    const { config: harnessConfig } = await getConfig(projectRoot);
+    const cliArgs = getAdditionalCliArgs();
+    const selectedRunner = getHarnessRunner(harnessConfig, cliArgs);
+    const harness = await getHarness(selectedRunner);
+
+    try {
+      return await this._createInBandTestRun(
+        tests,
+        watcher,
+        harness,
+        onStart,
+        onResult,
+        onFailure
+      );
+    } finally {
+      harness.bridge.dispose();
+      await harness.environment.dispose();
+    }
+  }
+
+  async _createInBandTestRun(
+    tests: Array<Test>,
+    watcher: TestWatcher,
+    harness: Harness,
+    onStart: OnTestStart,
+    onResult: OnTestSuccess,
+    onFailure: OnTestFailure
+  ): Promise<void> {
+    const mutex = pLimit(1);
+    let isFirstTest = true;
+
+    return tests.reduce(
+      (promise, test) =>
+        mutex(() =>
+          promise
+            .then(async () => {
+              if (watcher.isInterrupted()) {
+                throw new CancelRun();
+              }
+
+              if (!isFirstTest) {
+                await new Promise((resolve) => {
+                  harness.bridge.once('ready', resolve);
+                  harness.environment.restart();
+                });
+              }
+              isFirstTest = false;
+
+              return onStart(test).then(() =>
+                runHarnessTestFile({
+                  testPath: test.path,
+                  harness,
+                  globalConfig: this.#globalConfig,
+                  projectConfig: test.context.config,
+                })
+              );
+            })
+            .then((result) => onResult(test, result))
+            .catch((err) => onFailure(test, err))
+        ),
+      Promise.resolve()
+    );
+  }
+}