diff --git a/packages/compiler-cli/ngcc/src/execution/cluster/executor.ts b/packages/compiler-cli/ngcc/src/execution/cluster/executor.ts
index 333a8e4e72..b595b07781 100644
--- a/packages/compiler-cli/ngcc/src/execution/cluster/executor.ts
+++ b/packages/compiler-cli/ngcc/src/execution/cluster/executor.ts
@@ -5,11 +5,7 @@
  * Use of this source code is governed by an MIT-style license that can be
  * found in the LICENSE file at https://angular.io/license
  */
-
-/// <reference types="node" />
-
-import * as cluster from 'cluster';
-
+import {FileSystem} from '../../../../src/ngtsc/file_system';
 import {AsyncLocker} from '../../locking/async_locker';
 import {Logger} from '../../logging/logger';
 import {PackageJsonUpdater} from '../../writing/package_json_updater';
@@ -17,8 +13,6 @@ import {AnalyzeEntryPointsFn, CreateCompileFn, Executor} from '../api';
 import {CreateTaskCompletedCallback} from '../tasks/api';
 
 import {ClusterMaster} from './master';
-import {ClusterWorker} from './worker';
-
 
 /**
  * An `Executor` that processes tasks in parallel (on multiple processes) and completes
@@ -26,26 +20,19 @@ import {ClusterWorker} from './worker';
  */
 export class ClusterExecutor implements Executor {
   constructor(
-      private workerCount: number, private logger: Logger,
+      private workerCount: number, private fileSystem: FileSystem, private logger: Logger,
       private pkgJsonUpdater: PackageJsonUpdater, private lockFile: AsyncLocker,
       private createTaskCompletedCallback: CreateTaskCompletedCallback) {}
 
-  async execute(analyzeEntryPoints: AnalyzeEntryPointsFn, createCompileFn: CreateCompileFn):
+  async execute(analyzeEntryPoints: AnalyzeEntryPointsFn, _createCompileFn: CreateCompileFn):
       Promise<void> {
-    if (cluster.isMaster) {
-      // This process is the cluster master.
-      return this.lockFile.lock(() => {
-        this.logger.debug(`Running ngcc on ${this.constructor.name} (using ${
-            this.workerCount} worker processes).`);
-        const master = new ClusterMaster(
-            this.workerCount, this.logger, this.pkgJsonUpdater, analyzeEntryPoints,
-            this.createTaskCompletedCallback);
-        return master.run();
-      });
-    } else {
-      // This process is a cluster worker.
-      const worker = new ClusterWorker(this.logger, createCompileFn);
-      return worker.run();
-    }
+    return this.lockFile.lock(() => {
+      this.logger.debug(
+          `Running ngcc on ${this.constructor.name} (using ${this.workerCount} worker processes).`);
+      const master = new ClusterMaster(
+          this.workerCount, this.fileSystem, this.logger, this.pkgJsonUpdater, analyzeEntryPoints,
+          this.createTaskCompletedCallback);
+      return master.run();
+    });
   }
 }
diff --git a/packages/compiler-cli/ngcc/src/execution/cluster/master.ts b/packages/compiler-cli/ngcc/src/execution/cluster/master.ts
index e40e42009a..669960612e 100644
--- a/packages/compiler-cli/ngcc/src/execution/cluster/master.ts
+++ b/packages/compiler-cli/ngcc/src/execution/cluster/master.ts
@@ -10,7 +10,7 @@
 
 import * as cluster from 'cluster';
 
-import {resolve} from '../../../../src/ngtsc/file_system';
+import {FileSystem} from '../../../../src/ngtsc/file_system';
 import {Logger} from '../../logging/logger';
 import {PackageJsonUpdater} from '../../writing/package_json_updater';
 import {AnalyzeEntryPointsFn} from '../api';
@@ -33,13 +33,16 @@ export class ClusterMaster {
   private onTaskCompleted: TaskCompletedCallback;
 
   constructor(
-      private maxWorkerCount: number, private logger: Logger,
+      private maxWorkerCount: number, private fileSystem: FileSystem, private logger: Logger,
       private pkgJsonUpdater: PackageJsonUpdater, analyzeEntryPoints: AnalyzeEntryPointsFn,
       createTaskCompletedCallback: CreateTaskCompletedCallback) {
     if (!cluster.isMaster) {
       throw new Error('Tried to instantiate `ClusterMaster` on a worker process.');
     }
 
+    // Set the worker entry-point
+    cluster.setupMaster({exec: this.fileSystem.resolve(__dirname, 'worker.js')});
+
     this.taskQueue = analyzeEntryPoints();
     this.onTaskCompleted = createTaskCompletedCallback(this.taskQueue);
   }
@@ -227,7 +230,7 @@ export class ClusterMaster {
           JSON.stringify(msg));
     }
 
-    const expectedPackageJsonPath = resolve(task.entryPoint.path, 'package.json');
+    const expectedPackageJsonPath = this.fileSystem.resolve(task.entryPoint.path, 'package.json');
     const parsedPackageJson = task.entryPoint.packageJson;
 
     if (expectedPackageJsonPath !== msg.packageJsonPath) {
diff --git a/packages/compiler-cli/ngcc/src/execution/cluster/worker.ts b/packages/compiler-cli/ngcc/src/execution/cluster/worker.ts
index 24b6a3745c..e58a5326d1 100644
--- a/packages/compiler-cli/ngcc/src/execution/cluster/worker.ts
+++ b/packages/compiler-cli/ngcc/src/execution/cluster/worker.ts
@@ -5,58 +5,102 @@
  * Use of this source code is governed by an MIT-style license that can be
  * found in the LICENSE file at https://angular.io/license
  */
-
 /// <reference types="node" />
 
 import * as cluster from 'cluster';
 
-import {Logger} from '../../logging/logger';
-import {CompileFn, CreateCompileFn} from '../api';
+import {absoluteFrom, CachedFileSystem, getFileSystem, NodeJSFileSystem, setFileSystem} from '../../../../src/ngtsc/file_system';
+import {readConfiguration} from '../../../../src/perform_compile';
+import {parseCommandLineOptions} from '../../command_line_options';
+import {ConsoleLogger} from '../../logging/console_logger';
+import {Logger, LogLevel} from '../../logging/logger';
+import {getPathMappingsFromTsConfig} from '../../utils';
+import {DirectPackageJsonUpdater} from '../../writing/package_json_updater';
+import {CreateCompileFn} from '../api';
+import {getCreateCompileFn} from '../create_compile_function';
 import {stringifyTask} from '../tasks/utils';
 
 import {MessageToWorker} from './api';
+import {ClusterPackageJsonUpdater} from './package_json_updater';
 import {sendMessageToMaster} from './utils';
 
-
-/**
- * A cluster worker is responsible for processing one task (i.e. one format property for a specific
- * entry-point) at a time and reporting results back to the cluster master.
- */
-export class ClusterWorker {
-  private compile: CompileFn;
-
-  constructor(private logger: Logger, createCompileFn: CreateCompileFn) {
-    if (cluster.isMaster) {
-      throw new Error('Tried to instantiate `ClusterWorker` on the master process.');
-    }
-
-    this.compile = createCompileFn(
-        (_task, outcome, message) =>
-            sendMessageToMaster({type: 'task-completed', outcome, message}));
-  }
-
-  run(): Promise<void> {
-    // Listen for `ProcessTaskMessage`s and process tasks.
-    cluster.worker.on('message', (msg: MessageToWorker) => {
-      try {
-        switch (msg.type) {
-          case 'process-task':
-            this.logger.debug(
-                `[Worker #${cluster.worker.id}] Processing task: ${stringifyTask(msg.task)}`);
-            return this.compile(msg.task);
-          default:
-            throw new Error(
-                `[Worker #${cluster.worker.id}] Invalid message received: ${JSON.stringify(msg)}`);
-        }
-      } catch (err) {
-        sendMessageToMaster({
-          type: 'error',
-          error: (err instanceof Error) ? (err.stack || err.message) : err,
-        });
+// Cluster worker entry point
+if (require.main === module) {
+  process.title = 'ngcc (worker)';
+  setFileSystem(new CachedFileSystem(new NodeJSFileSystem()));
+  let {
+    basePath,
+    targetEntryPointPath,
+    createNewEntryPointFormats = false,
+    logger = new ConsoleLogger(LogLevel.info),
+    pathMappings,
+    errorOnFailedEntryPoint = false,
+    enableI18nLegacyMessageIdFormat = true,
+    tsConfigPath
+  } = parseCommandLineOptions(process.argv.slice(2));
+  (async () => {
+    try {
+      if (!!targetEntryPointPath) {
+        // targetEntryPointPath forces us to error if an entry-point fails.
+        errorOnFailedEntryPoint = true;
       }
-    });
 
-    // Return a promise that is never resolved.
-    return new Promise(() => undefined);
-  }
+      const fileSystem = getFileSystem();
+      const absBasePath = absoluteFrom(basePath);
+      const projectPath = fileSystem.dirname(absBasePath);
+      const tsConfig =
+          tsConfigPath !== null ? readConfiguration(tsConfigPath || projectPath) : null;
+
+      if (pathMappings === undefined) {
+        pathMappings = getPathMappingsFromTsConfig(tsConfig, projectPath);
+      }
+
+      const pkgJsonUpdater =
+          new ClusterPackageJsonUpdater(new DirectPackageJsonUpdater(fileSystem));
+
+      // The function for creating the `compile()` function.
+      const createCompileFn = getCreateCompileFn(
+          fileSystem, logger, pkgJsonUpdater, createNewEntryPointFormats, errorOnFailedEntryPoint,
+          enableI18nLegacyMessageIdFormat, tsConfig, pathMappings);
+
+      await startWorker(logger, createCompileFn);
+      process.exitCode = 0;
+    } catch (e) {
+      console.error(e.stack || e.message);
+      process.exitCode = 1;
+    }
+  })();
 }
+
+export async function startWorker(logger: Logger, createCompileFn: CreateCompileFn): Promise<void> {
+  if (cluster.isMaster) {
+    throw new Error('Tried to run cluster worker on the master process.');
+  }
+
+  const compile = createCompileFn(
+      (_task, outcome, message) => sendMessageToMaster({type: 'task-completed', outcome, message}));
+
+
+  // Listen for `ProcessTaskMessage`s and process tasks.
+  cluster.worker.on('message', (msg: MessageToWorker) => {
+    try {
+      switch (msg.type) {
+        case 'process-task':
+          logger.debug(
+              `[Worker #${cluster.worker.id}] Processing task: ${stringifyTask(msg.task)}`);
+          return compile(msg.task);
+        default:
+          throw new Error(
+              `[Worker #${cluster.worker.id}] Invalid message received: ${JSON.stringify(msg)}`);
+      }
+    } catch (err) {
+      sendMessageToMaster({
+        type: 'error',
+        error: (err instanceof Error) ? (err.stack || err.message) : err,
+      });
+    }
+  });
+
+  // Return a promise that is never resolved.
+  return new Promise(() => undefined);
+}
\ No newline at end of file
diff --git a/packages/compiler-cli/ngcc/src/main.ts b/packages/compiler-cli/ngcc/src/main.ts
index bdcaa2a19e..33fff60680 100644
--- a/packages/compiler-cli/ngcc/src/main.ts
+++ b/packages/compiler-cli/ngcc/src/main.ts
@@ -178,7 +178,7 @@ function getExecutor(
       // Execute in parallel. Use up to 8 CPU cores for workers, always reserving one for master.
       const workerCount = Math.min(8, os.cpus().length - 1);
       return new ClusterExecutor(
-          workerCount, logger, pkgJsonUpdater, locker, createTaskCompletedCallback);
+          workerCount, fileSystem, logger, pkgJsonUpdater, locker, createTaskCompletedCallback);
     } else {
       // Execute serially, on a single thread (async).
       return new SingleProcessExecutorAsync(logger, locker, createTaskCompletedCallback);
diff --git a/packages/compiler-cli/ngcc/test/BUILD.bazel b/packages/compiler-cli/ngcc/test/BUILD.bazel
index ccafbae4fd..320d64646a 100644
--- a/packages/compiler-cli/ngcc/test/BUILD.bazel
+++ b/packages/compiler-cli/ngcc/test/BUILD.bazel
@@ -29,6 +29,7 @@ ts_library(
         "@npm//magic-string",
         "@npm//sourcemap-codec",
         "@npm//typescript",
+        "@npm//yargs",
     ],
 )
 
diff --git a/packages/compiler-cli/ngcc/test/execution/cluster/executor_spec.ts b/packages/compiler-cli/ngcc/test/execution/cluster/executor_spec.ts
index c5f7f64fe7..1def235e51 100644
--- a/packages/compiler-cli/ngcc/test/execution/cluster/executor_spec.ts
+++ b/packages/compiler-cli/ngcc/test/execution/cluster/executor_spec.ts
@@ -8,47 +8,44 @@
 
 /// <reference types="node" />
 
+import {getFileSystem} from '@angular/compiler-cli/src/ngtsc/file_system';
 import * as cluster from 'cluster';
 
-import {MockFileSystemNative} from '../../../../src/ngtsc/file_system/testing';
+import {MockFileSystemNative, runInEachFileSystem} from '../../../../src/ngtsc/file_system/testing';
 import {ClusterExecutor} from '../../../src/execution/cluster/executor';
 import {ClusterMaster} from '../../../src/execution/cluster/master';
-import {ClusterWorker} from '../../../src/execution/cluster/worker';
 import {AsyncLocker} from '../../../src/locking/async_locker';
 import {PackageJsonUpdater} from '../../../src/writing/package_json_updater';
 import {MockLockFile} from '../../helpers/mock_lock_file';
 import {MockLogger} from '../../helpers/mock_logger';
 import {mockProperty} from '../../helpers/spy_utils';
 
+runInEachFileSystem(() => {
+  describe('ClusterExecutor', () => {
+    const runAsClusterMaster = mockProperty(cluster, 'isMaster');
+    let masterRunSpy: jasmine.Spy;
+    let mockLogger: MockLogger;
+    let lockFileLog: string[];
+    let mockLockFile: MockLockFile;
+    let locker: AsyncLocker;
+    let executor: ClusterExecutor;
+    let createTaskCompletedCallback: jasmine.Spy;
 
-describe('ClusterExecutor', () => {
-  const runAsClusterMaster = mockProperty(cluster, 'isMaster');
-  let masterRunSpy: jasmine.Spy;
-  let workerRunSpy: jasmine.Spy;
-  let mockLogger: MockLogger;
-  let lockFileLog: string[];
-  let mockLockFile: MockLockFile;
-  let locker: AsyncLocker;
-  let executor: ClusterExecutor;
-  let createTaskCompletedCallback: jasmine.Spy;
+    beforeEach(() => {
+      masterRunSpy = spyOn(ClusterMaster.prototype, 'run')
+                         .and.returnValue(Promise.resolve('CusterMaster#run()' as any));
+      createTaskCompletedCallback = jasmine.createSpy('createTaskCompletedCallback');
 
-  beforeEach(() => {
-    masterRunSpy = spyOn(ClusterMaster.prototype, 'run')
-                       .and.returnValue(Promise.resolve('CusterMaster#run()' as any));
-    workerRunSpy = spyOn(ClusterWorker.prototype, 'run')
-                       .and.returnValue(Promise.resolve('CusterWorker#run()' as any));
-    createTaskCompletedCallback = jasmine.createSpy('createTaskCompletedCallback');
+      mockLogger = new MockLogger();
+      lockFileLog = [];
+      mockLockFile = new MockLockFile(new MockFileSystemNative(), lockFileLog);
+      locker = new AsyncLocker(mockLockFile, mockLogger, 200, 2);
+      executor = new ClusterExecutor(
+          42, getFileSystem(), mockLogger, null as unknown as PackageJsonUpdater, locker,
+          createTaskCompletedCallback);
+    });
 
-    mockLogger = new MockLogger();
-    lockFileLog = [];
-    mockLockFile = new MockLockFile(new MockFileSystemNative(), lockFileLog);
-    locker = new AsyncLocker(mockLockFile, mockLogger, 200, 2);
-    executor = new ClusterExecutor(
-        42, mockLogger, null as unknown as PackageJsonUpdater, locker, createTaskCompletedCallback);
-  });
-
-  describe('execute()', () => {
-    describe('(on cluster master)', () => {
+    describe('execute()', () => {
       beforeEach(() => runAsClusterMaster(true));
 
       it('should log debug info about the executor', async () => {
@@ -68,7 +65,6 @@ describe('ClusterExecutor', () => {
             .toBe('CusterMaster#run()' as any);
 
         expect(masterRunSpy).toHaveBeenCalledWith();
-        expect(workerRunSpy).not.toHaveBeenCalled();
 
         expect(analyzeEntryPointsSpy).toHaveBeenCalledWith();
         expect(createCompilerFnSpy).not.toHaveBeenCalled();
@@ -102,7 +98,7 @@ describe('ClusterExecutor', () => {
         });
 
         executor = new ClusterExecutor(
-            42, mockLogger, null as unknown as PackageJsonUpdater, locker,
+            42, getFileSystem(), mockLogger, null as unknown as PackageJsonUpdater, locker,
             createTaskCompletedCallback);
         let error = '';
         try {
@@ -122,7 +118,7 @@ describe('ClusterExecutor', () => {
         });
 
         executor = new ClusterExecutor(
-            42, mockLogger, null as unknown as PackageJsonUpdater, locker,
+            42, getFileSystem(), mockLogger, null as unknown as PackageJsonUpdater, locker,
             createTaskCompletedCallback);
         let error = '';
         try {
@@ -135,36 +131,5 @@ describe('ClusterExecutor', () => {
         expect(masterRunSpy).toHaveBeenCalled();
       });
     });
-
-    describe('(on cluster worker)', () => {
-      beforeEach(() => runAsClusterMaster(false));
-
-      it('should not log debug info about the executor', async () => {
-        const anyFn: () => any = () => undefined;
-        await executor.execute(anyFn, anyFn);
-
-        expect(mockLogger.logs.debug).toEqual([]);
-      });
-
-      it('should delegate to `ClusterWorker#run()`', async () => {
-        const analyzeEntryPointsSpy = jasmine.createSpy('analyzeEntryPoints');
-        const createCompilerFnSpy = jasmine.createSpy('createCompilerFn');
-
-        expect(await executor.execute(analyzeEntryPointsSpy, createCompilerFnSpy))
-            .toBe('CusterWorker#run()' as any);
-
-        expect(masterRunSpy).not.toHaveBeenCalledWith();
-        expect(workerRunSpy).toHaveBeenCalled();
-
-        expect(analyzeEntryPointsSpy).not.toHaveBeenCalled();
-        expect(createCompilerFnSpy).toHaveBeenCalledWith(jasmine.any(Function));
-      });
-
-      it('should not call LockFile.write() or LockFile.remove()', async () => {
-        const anyFn: () => any = () => undefined;
-        await executor.execute(anyFn, anyFn);
-        expect(lockFileLog).toEqual([]);
-      });
-    });
   });
 });
diff --git a/packages/compiler-cli/ngcc/test/execution/cluster/worker_spec.ts b/packages/compiler-cli/ngcc/test/execution/cluster/worker_spec.ts
index b9d92e47d9..8cc9370b3c 100644
--- a/packages/compiler-cli/ngcc/test/execution/cluster/worker_spec.ts
+++ b/packages/compiler-cli/ngcc/test/execution/cluster/worker_spec.ts
@@ -11,13 +11,13 @@
 import * as cluster from 'cluster';
 import {EventEmitter} from 'events';
 
-import {ClusterWorker} from '../../../src/execution/cluster/worker';
+import {startWorker} from '../../../src/execution/cluster/worker';
 import {Task, TaskCompletedCallback, TaskProcessingOutcome} from '../../../src/execution/tasks/api';
 import {MockLogger} from '../../helpers/mock_logger';
 import {mockProperty} from '../../helpers/spy_utils';
 
 
-describe('ClusterWorker', () => {
+describe('startWorker()', () => {
   const runAsClusterMaster = mockProperty(cluster, 'isMaster');
   const mockProcessSend = mockProperty(process, 'send');
   let processSendSpy: jasmine.Spy;
@@ -35,131 +35,116 @@ describe('ClusterWorker', () => {
     mockLogger = new MockLogger();
   });
 
-  describe('constructor()', () => {
-    describe('(on cluster master)', () => {
-      beforeEach(() => runAsClusterMaster(true));
+  describe('(on cluster master)', () => {
+    beforeEach(() => runAsClusterMaster(true));
 
-      it('should throw an error', () => {
-        expect(() => new ClusterWorker(mockLogger, createCompileFnSpy))
-            .toThrowError('Tried to instantiate `ClusterWorker` on the master process.');
-        expect(createCompileFnSpy).not.toHaveBeenCalled();
-      });
-    });
-
-    describe('(on cluster worker)', () => {
-      beforeEach(() => runAsClusterMaster(false));
-
-      it('should create the `compileFn()`', () => {
-        new ClusterWorker(mockLogger, createCompileFnSpy);
-        expect(createCompileFnSpy).toHaveBeenCalledWith(jasmine.any(Function));
-      });
-
-      it('should set up `compileFn()` to send `task-completed` messages to master', () => {
-        new ClusterWorker(mockLogger, createCompileFnSpy);
-        const onTaskCompleted: TaskCompletedCallback = createCompileFnSpy.calls.argsFor(0)[0];
-
-        onTaskCompleted(null as any, TaskProcessingOutcome.Processed, null);
-        expect(processSendSpy).toHaveBeenCalledTimes(1);
-        expect(processSendSpy)
-            .toHaveBeenCalledWith(
-                {type: 'task-completed', outcome: TaskProcessingOutcome.Processed, message: null});
-
-        processSendSpy.calls.reset();
-
-        onTaskCompleted(null as any, TaskProcessingOutcome.Failed, 'error message');
-        expect(processSendSpy).toHaveBeenCalledTimes(1);
-        expect(processSendSpy).toHaveBeenCalledWith({
-          type: 'task-completed',
-          outcome: TaskProcessingOutcome.Failed,
-          message: 'error message',
-        });
-      });
+    it('should throw an error', async () => {
+      await expectAsync(startWorker(mockLogger, createCompileFnSpy))
+          .toBeRejectedWithError('Tried to run cluster worker on the master process.');
+      expect(createCompileFnSpy).not.toHaveBeenCalled();
     });
   });
 
-  describe('run()', () => {
-    describe(
-        '(on cluster master)',
-        () => {/* No tests needed, becasue the constructor would have thrown. */});
+  describe('(on cluster worker)', () => {
+    // The `cluster.worker` property is normally `undefined` on the master process and set to the
+    // current `cluster.worker` on worker processes.
+    const mockClusterWorker = mockProperty(cluster, 'worker');
 
-    describe('(on cluster worker)', () => {
-      // The `cluster.worker` property is normally `undefined` on the master process and set to the
-      // current `cluster.Worker` on worker processes.
-      const mockClusterWorker = mockProperty(cluster, 'worker');
-      let worker: ClusterWorker;
+    beforeEach(() => {
+      runAsClusterMaster(false);
+      mockClusterWorker(Object.assign(new EventEmitter(), {id: 42}) as cluster.Worker);
+    });
 
-      beforeEach(() => {
-        runAsClusterMaster(false);
-        mockClusterWorker(Object.assign(new EventEmitter(), {id: 42}) as cluster.Worker);
+    it('should create the `compileFn()`', () => {
+      startWorker(mockLogger, createCompileFnSpy);
+      expect(createCompileFnSpy).toHaveBeenCalledWith(jasmine.any(Function));
+    });
 
-        worker = new ClusterWorker(mockLogger, createCompileFnSpy);
+    it('should set up `compileFn()` to send `task-completed` messages to master', () => {
+      startWorker(mockLogger, createCompileFnSpy);
+      const onTaskCompleted: TaskCompletedCallback = createCompileFnSpy.calls.argsFor(0)[0];
+
+      onTaskCompleted(null as any, TaskProcessingOutcome.Processed, null);
+      expect(processSendSpy).toHaveBeenCalledTimes(1);
+      expect(processSendSpy)
+          .toHaveBeenCalledWith(
+              {type: 'task-completed', outcome: TaskProcessingOutcome.Processed, message: null});
+
+      processSendSpy.calls.reset();
+
+      onTaskCompleted(null as any, TaskProcessingOutcome.Failed, 'error message');
+      expect(processSendSpy).toHaveBeenCalledTimes(1);
+      expect(processSendSpy).toHaveBeenCalledWith({
+        type: 'task-completed',
+        outcome: TaskProcessingOutcome.Failed,
+        message: 'error message',
+      });
+    });
+
+    it('should return a promise (that is never resolved)', done => {
+      const promise = startWorker(mockLogger, createCompileFnSpy);
+
+      expect(promise).toEqual(jasmine.any(Promise));
+
+      promise.then(
+          () => done.fail('Expected promise not to resolve'),
+          () => done.fail('Expected promise not to reject'));
+
+      // We can't wait forever to verify that the promise is not resolved, but at least verify
+      // that it is not resolved immediately.
+      setTimeout(done, 100);
+    });
+
+    it('should handle `process-task` messages', () => {
+      const mockTask = {
+        entryPoint: {name: 'foo'},
+        formatProperty: 'es2015',
+        processDts: true,
+      } as unknown as Task;
+
+      startWorker(mockLogger, createCompileFnSpy);
+      cluster.worker.emit('message', {type: 'process-task', task: mockTask});
+
+      expect(compileFnSpy).toHaveBeenCalledWith(mockTask);
+      expect(processSendSpy).not.toHaveBeenCalled();
+
+      expect(mockLogger.logs.debug[0]).toEqual([
+        '[Worker #42] Processing task: {entryPoint: foo, formatProperty: es2015, processDts: true}',
+      ]);
+    });
+
+    it('should send errors during task processing back to the master process', () => {
+      const mockTask = {
+        entryPoint: {name: 'foo'},
+        formatProperty: 'es2015',
+        processDts: true,
+      } as unknown as Task;
+
+      let err: string|Error;
+      compileFnSpy.and.callFake(() => {
+        throw err;
       });
 
-      it('should return a promise (that is never resolved)', done => {
-        const promise = worker.run();
+      startWorker(mockLogger, createCompileFnSpy);
 
-        expect(promise).toEqual(jasmine.any(Promise));
+      err = 'Error string.';
+      cluster.worker.emit('message', {type: 'process-task', task: mockTask});
+      expect(processSendSpy).toHaveBeenCalledWith({type: 'error', error: err});
 
-        promise.then(
-            () => done.fail('Expected promise not to resolve'),
-            () => done.fail('Expected promise not to reject'));
+      err = new Error('Error object.');
+      cluster.worker.emit('message', {type: 'process-task', task: mockTask});
+      expect(processSendSpy).toHaveBeenCalledWith({type: 'error', error: err.stack});
+    });
 
-        // We can't wait forever to verify that the promise is not resolved, but at least verify
-        // that it is not resolved immediately.
-        setTimeout(done, 100);
-      });
+    it('should throw, when an unknown message type is received', () => {
+      startWorker(mockLogger, createCompileFnSpy);
+      cluster.worker.emit('message', {type: 'unknown', foo: 'bar'});
 
-      it('should handle `process-task` messages', () => {
-        const mockTask = {
-          entryPoint: {name: 'foo'},
-          formatProperty: 'es2015',
-          processDts: true,
-        } as unknown as Task;
-
-        worker.run();
-        cluster.worker.emit('message', {type: 'process-task', task: mockTask});
-
-        expect(compileFnSpy).toHaveBeenCalledWith(mockTask);
-        expect(processSendSpy).not.toHaveBeenCalled();
-
-        expect(mockLogger.logs.debug[0]).toEqual([
-          '[Worker #42] Processing task: {entryPoint: foo, formatProperty: es2015, processDts: true}',
-        ]);
-      });
-
-      it('should send errors during task processing back to the master process', () => {
-        const mockTask = {
-          entryPoint: {name: 'foo'},
-          formatProperty: 'es2015',
-          processDts: true,
-        } as unknown as Task;
-
-        let err: string|Error;
-        compileFnSpy.and.callFake(() => {
-          throw err;
-        });
-
-        worker.run();
-
-        err = 'Error string.';
-        cluster.worker.emit('message', {type: 'process-task', task: mockTask});
-        expect(processSendSpy).toHaveBeenCalledWith({type: 'error', error: err});
-
-        err = new Error('Error object.');
-        cluster.worker.emit('message', {type: 'process-task', task: mockTask});
-        expect(processSendSpy).toHaveBeenCalledWith({type: 'error', error: err.stack});
-      });
-
-      it('should throw, when an unknown message type is received', () => {
-        worker.run();
-        cluster.worker.emit('message', {type: 'unknown', foo: 'bar'});
-
-        expect(compileFnSpy).not.toHaveBeenCalled();
-        expect(processSendSpy).toHaveBeenCalledWith({
-          type: 'error',
-          error: jasmine.stringMatching(
-              'Error: \\[Worker #42\\] Invalid message received: {"type":"unknown","foo":"bar"}'),
-        });
+      expect(compileFnSpy).not.toHaveBeenCalled();
+      expect(processSendSpy).toHaveBeenCalledWith({
+        type: 'error',
+        error: jasmine.stringMatching(
+            'Error: \\[Worker #42\\] Invalid message received: {"type":"unknown","foo":"bar"}'),
       });
     });
   });