fix: worker being killed after being spawned and other worker bugs

e2e/__tests__/worker-restarting.test.ts

@@ -0,0 +1,16 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+import {extractSummary} from '../Utils';
+import runJest from '../runJest';
+
+it('all 3 test files should complete', () => {
+  const result = runJest('worker-restating');
+  expect(result.exitCode).toBe(0);
+  const {summary} = extractSummary(result.stderr);
+  expect(summary).toMatchSnapshot();
+});

e2e/worker-restarting/__tests__/test1.js

@@ -0,0 +1,10 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+test('basic test', () => {
+  expect(true).toBeTruthy();
+});

e2e/worker-restarting/__tests__/test2.js

@@ -0,0 +1,10 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+test('basic test', () => {
+  expect(true).toBeTruthy();
+});

e2e/worker-restarting/__tests__/test3.js

@@ -0,0 +1,10 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+test('basic test', () => {
+  expect(true).toBeTruthy();
+});

e2e/worker-restarting/package.json

@@ -0,0 +1,6 @@
+{
+  "jest": {
+    "maxWorkers": 2,
+    "workerIdleMemoryLimit": "1MB"
+  }
+}

packages/jest-worker/src/types.ts

@@ -66,12 +66,15 @@ export interface WorkerPoolInterface {
 }
 
 export interface WorkerInterface {
+  get state(): WorkerStates;
+
   send(
     request: ChildMessage,
     onProcessStart: OnStart,
     onProcessEnd: OnEnd,
     onCustomMessage: OnCustomMessage,
   ): void;
+
   waitForExit(): Promise<void>;
   forceExit(): void;
 
@@ -83,6 +86,18 @@ export interface WorkerInterface {
    */
   getWorkerSystemId(): number;
   getMemoryUsage(): Promise<number | null>;
+  /**
+   * Checks to see if the child worker is actually running.
+   */
+  isWorkerRunning(): boolean;
+  /**
+   * When the worker child is started and ready to start handling requests.
+   *
+   * @remarks
+   * This mostly exists to help with testing so that you don't check the status
+   * of things like isWorkerRunning before it actually is.
+   */
+  waitForWorkerReady(): Promise<void>;
 }
 
 export type PoolExitResult = {
@@ -170,8 +185,21 @@ export type WorkerOptions = {
    * the raw output of the worker.
    */
   silent?: boolean;
+  /**
+   * Used to immediately bind event handlers.
+   */
+  on?: {
+    [WorkerEvents.STATE_CHANGE]:
+      | onStateChangeHandler
+      | Array<onStateChangeHandler>;
+  };
 };
 
+export type onStateChangeHandler = (
+  state: WorkerStates,
+  oldState: WorkerStates,
+) => void;
+
 // Messages passed from the parent to the children.
 
 export type MessagePort = typeof EventEmitter & {
@@ -265,3 +293,7 @@ export enum WorkerStates {
   SHUTTING_DOWN = 'shutting-down',
   SHUT_DOWN = 'shut-down',
 }
+
+export enum WorkerEvents {
+  STATE_CHANGE = 'state-change',
+}