diff --git a/packages/service-worker/worker/src/service-worker.d.ts b/packages/service-worker/worker/src/service-worker.d.ts
index 7af223bc07..f01adabfe6 100644
--- a/packages/service-worker/worker/src/service-worker.d.ts
+++ b/packages/service-worker/worker/src/service-worker.d.ts
@@ -64,29 +64,24 @@ type WindowClientState = 'hidden'|'visible'|'prerender'|'unloaded';
 // Fetch API
 
 interface FetchEvent extends ExtendableEvent {
-  request: Request;
-  clientId?: string;
-  resultingClientId?: string;
-  respondWith(response: Promise<Response>|Response): Promise<Response>;
+  readonly clientId: string;
+  readonly preloadResponse: Promise<any>;
+  readonly request: Request;
+  readonly resultingClientId: string;
+  respondWith(r: Response|Promise<Response>): void;
 }
 
-interface InstallEvent extends ExtendableEvent {
-  activeWorker: ServiceWorker;
-}
-
-interface ActivateEvent extends ExtendableEvent {}
-
 // Notification API
 
 interface NotificationEvent extends ExtendableEvent {
-  action: string;
-  notification: Notification;
+  readonly action: string;
+  readonly notification: Notification;
 }
 
 // Push API
 
 interface PushEvent extends ExtendableEvent {
-  data: PushMessageData;
+  readonly data: PushMessageData|null;
 }
 
 interface PushMessageData {
@@ -99,13 +94,16 @@ interface PushMessageData {
 // Sync API
 
 interface SyncEvent extends ExtendableEvent {
-  lastChance: boolean;
-  tag: string;
+  readonly lastChance: boolean;
+  readonly tag: string;
 }
 
 interface ExtendableMessageEvent extends ExtendableEvent {
-  data: any;
-  source: Client|Object;
+  readonly data: any;
+  readonly lastEventId: string;
+  readonly origin: string;
+  readonly ports: ReadonlyArray<MessagePort>;
+  readonly source: Client|ServiceWorker|MessagePort|null;
 }
 
 // ServiceWorkerGlobalScope
diff --git a/packages/service-worker/worker/test/happy_spec.ts b/packages/service-worker/worker/test/happy_spec.ts
index 0a9561dcf2..fafff3990b 100644
--- a/packages/service-worker/worker/test/happy_spec.ts
+++ b/packages/service-worker/worker/test/happy_spec.ts
@@ -783,7 +783,7 @@ describe('Driver', () => {
       const message: any = scope.clients.getMock('default')!.messages[0];
 
       expect(message.type).toEqual('NOTIFICATION_CLICK');
-      expect(message.data.action).toBeUndefined();
+      expect(message.data.action).toBe('');
       expect(message.data.notification.title).toEqual('This is a test without action');
       expect(message.data.notification.body).toEqual('Test body without action');
     });
diff --git a/packages/service-worker/worker/testing/events.ts b/packages/service-worker/worker/testing/events.ts
index f42c1698a0..bedd3a7ce1 100644
--- a/packages/service-worker/worker/testing/events.ts
+++ b/packages/service-worker/worker/testing/events.ts
@@ -49,7 +49,7 @@ export class MockEvent implements Event {
 }
 
 export class MockExtendableEvent extends MockEvent implements ExtendableEvent {
-  private queue: Promise<void>[] = [];
+  private queue: Promise<unknown>[] = [];
 
   get ready(): Promise<void> {
     return (async () => {
@@ -59,7 +59,7 @@ export class MockExtendableEvent extends MockEvent implements ExtendableEvent {
     })();
   }
 
-  waitUntil(promise: Promise<void>): void {
+  waitUntil(promise: Promise<unknown>): void {
     this.queue.push(promise);
   }
 }
@@ -70,7 +70,8 @@ export class MockActivateEvent extends MockExtendableEvent {
   }
 }
 
-export class MockFetchEvent extends MockExtendableEvent {
+export class MockFetchEvent extends MockExtendableEvent implements FetchEvent {
+  readonly preloadResponse = Promise.resolve();
   response: Promise<Response|undefined> = Promise.resolve(undefined);
 
   constructor(
@@ -78,9 +79,8 @@ export class MockFetchEvent extends MockExtendableEvent {
     super('fetch');
   }
 
-  respondWith(promise: Promise<Response>): Promise<Response> {
-    this.response = promise;
-    return promise;
+  respondWith(r: Response|Promise<Response>): void {
+    this.response = Promise.resolve(r);
   }
 }
 
@@ -90,27 +90,33 @@ export class MockInstallEvent extends MockExtendableEvent {
   }
 }
 
-export class MockMessageEvent extends MockExtendableEvent {
-  constructor(readonly data: Object, readonly source: MockClient|null) {
+export class MockExtendableMessageEvent extends MockExtendableEvent implements
+    ExtendableMessageEvent {
+  readonly lastEventId = '';
+  readonly origin = '';
+  readonly ports: ReadonlyArray<MessagePort> = [];
+
+  constructor(readonly data: any, readonly source: Client|MessagePort|ServiceWorker|null) {
     super('message');
   }
 }
 
-export class MockNotificationEvent extends MockExtendableEvent {
+export class MockNotificationEvent extends MockExtendableEvent implements NotificationEvent {
   readonly notification = {
     ...this._notification,
     close: () => undefined,
-  };
+  } as Notification;
 
-  constructor(private _notification: any, readonly action?: string) {
+  constructor(private _notification: Partial<Notification>, readonly action = '') {
     super('notification');
   }
 }
 
-export class MockPushEvent extends MockExtendableEvent {
-  data = {
+export class MockPushEvent extends MockExtendableEvent implements PushEvent {
+  readonly data = {
     json: () => this._data,
-  };
+    text: () => JSON.stringify(this._data),
+  } as PushMessageData;
 
   constructor(private _data: object) {
     super('push');
diff --git a/packages/service-worker/worker/testing/scope.ts b/packages/service-worker/worker/testing/scope.ts
index 2619a8de94..3dd0dcac5b 100644
--- a/packages/service-worker/worker/testing/scope.ts
+++ b/packages/service-worker/worker/testing/scope.ts
@@ -13,7 +13,7 @@ import {AssetGroupConfig, Manifest} from '../src/manifest';
 import {sha1} from '../src/sha1';
 
 import {MockCacheStorage} from './cache';
-import {MockActivateEvent, MockFetchEvent, MockInstallEvent, MockMessageEvent, MockNotificationEvent, MockPushEvent} from './events';
+import {MockActivateEvent, MockExtendableMessageEvent, MockFetchEvent, MockInstallEvent, MockNotificationEvent, MockPushEvent} from './events';
 import {MockHeaders, MockRequest, MockResponse} from './fetch';
 import {MockServerState, MockServerStateBuilder} from './mock';
 import {normalizeUrl, parseUrl} from './utils';
@@ -244,12 +244,13 @@ export class SwTestHarness extends Adapter<MockCacheStorage> implements ServiceW
     if (!this.eventHandlers.has('message')) {
       throw new Error('No message handler registered');
     }
-    let event: MockMessageEvent;
+    let event: MockExtendableMessageEvent;
     if (clientId === null) {
-      event = new MockMessageEvent(data, null);
+      event = new MockExtendableMessageEvent(data, null);
     } else {
       this.clients.add(clientId);
-      event = new MockMessageEvent(data, this.clients.getMock(clientId) || null);
+      event = new MockExtendableMessageEvent(
+          data, this.clients.getMock(clientId) as unknown as Client || null);
     }
     this.eventHandlers.get('message')!.call(this, event);
     return event.ready;