diff --git a/spec/helpers/marble-testing.ts b/spec/helpers/marble-testing.ts
index bb75d5b89c..3ba9927f5a 100644
--- a/spec/helpers/marble-testing.ts
+++ b/spec/helpers/marble-testing.ts
@@ -1,5 +1,5 @@
 import { Observable } from 'rxjs';
-import { SubscriptionLog } from '../../src/internal/testing/SubscriptionLog';
+import { SubscriptionLog } from '../../src/internal/testing/subscription-logging';
 import { ColdObservable } from '../../src/internal/testing/ColdObservable';
 import { HotObservable } from '../../src/internal/testing/HotObservable';
 import { observableToBeFn, subscriptionLogsToBeFn } from '../../src/internal/testing/TestScheduler';
diff --git a/src/internal/testing/ColdObservable.ts b/src/internal/testing/ColdObservable.ts
index 40cbe49a0a..845189039d 100644
--- a/src/internal/testing/ColdObservable.ts
+++ b/src/internal/testing/ColdObservable.ts
@@ -1,35 +1,30 @@
 import { Observable } from '../Observable';
 import { Subscription } from '../Subscription';
-import { Scheduler } from '../Scheduler';
 import { TestMessage } from './TestMessage';
-import { SubscriptionLog } from './SubscriptionLog';
-import { SubscriptionLoggable } from './SubscriptionLoggable';
-import { applyMixins } from '../util/applyMixins';
 import { Subscriber } from '../Subscriber';
 import { observeNotification } from '../Notification';
+import { SchedulerLike, TeardownLogic } from '../types';
+import { logSubscribedFrame, logUnsubscribedFrame, SubscriptionLog } from './subscription-logging';
 
-export class ColdObservable<T> extends Observable<T> implements SubscriptionLoggable {
+export class ColdObservable<T> extends Observable<T> {
   public subscriptions: SubscriptionLog[] = [];
-  scheduler: Scheduler;
-  // @ts-ignore: Property has no initializer and is not definitely assigned
-  logSubscribedFrame: () => number;
-  // @ts-ignore: Property has no initializer and is not definitely assigned
-  logUnsubscribedFrame: (index: number) => void;
+  logSubscribedFrame = logSubscribedFrame;
+  logUnsubscribedFrame = logUnsubscribedFrame;
 
-  constructor(public messages: TestMessage[], scheduler: Scheduler) {
-    super(function (this: Observable<T>, subscriber: Subscriber<any>) {
-      const observable: ColdObservable<T> = this as any;
-      const index = observable.logSubscribedFrame();
-      const subscription = new Subscription();
-      subscription.add(
-        new Subscription(() => {
-          observable.logUnsubscribedFrame(index);
-        })
-      );
-      observable.scheduleMessages(subscriber);
-      return subscription;
-    });
-    this.scheduler = scheduler;
+  protected _subscribe(subscriber: Subscriber<any>): TeardownLogic {
+    const index = this.logSubscribedFrame();
+    const subscription = new Subscription();
+    subscription.add(
+      new Subscription(() => {
+        this.logUnsubscribedFrame(index);
+      })
+    );
+    this.scheduleMessages(subscriber);
+    return subscription;
+  }
+
+  constructor(public messages: TestMessage[], public scheduler: SchedulerLike) {
+    super();
   }
 
   scheduleMessages(subscriber: Subscriber<any>) {
@@ -39,7 +34,10 @@ export class ColdObservable<T> extends Observable<T> implements SubscriptionLogg
       subscriber.add(
         this.scheduler.schedule(
           (state) => {
-            const { message: { notification }, subscriber: destination } = state!;
+            const {
+              message: { notification },
+              subscriber: destination,
+            } = state!;
             observeNotification(notification, destination);
           },
           message.frame,
@@ -49,4 +47,3 @@ export class ColdObservable<T> extends Observable<T> implements SubscriptionLogg
     }
   }
 }
-applyMixins(ColdObservable, [SubscriptionLoggable]);
diff --git a/src/internal/testing/HotObservable.ts b/src/internal/testing/HotObservable.ts
index c151480620..075c29d430 100644
--- a/src/internal/testing/HotObservable.ts
+++ b/src/internal/testing/HotObservable.ts
@@ -3,32 +3,27 @@ import { Subscriber } from '../Subscriber';
 import { Subscription } from '../Subscription';
 import { Scheduler } from '../Scheduler';
 import { TestMessage } from './TestMessage';
-import { SubscriptionLog } from './SubscriptionLog';
-import { SubscriptionLoggable } from './SubscriptionLoggable';
-import { applyMixins } from '../util/applyMixins';
 import { observeNotification } from '../Notification';
+import { logSubscribedFrame, logUnsubscribedFrame, SubscriptionLog } from './subscription-logging';
 
-export class HotObservable<T> extends Subject<T> implements SubscriptionLoggable {
+export class HotObservable<T> extends Subject<T> {
   public subscriptions: SubscriptionLog[] = [];
-  scheduler: Scheduler;
-  // @ts-ignore: Property has no initializer and is not definitely assigned
-  logSubscribedFrame: () => number;
-  // @ts-ignore: Property has no initializer and is not definitely assigned
-  logUnsubscribedFrame: (index: number) => void;
 
-  constructor(public messages: TestMessage[], scheduler: Scheduler) {
+  logSubscribedFrame = logSubscribedFrame;
+
+  logUnsubscribedFrame = logUnsubscribedFrame;
+
+  constructor(public messages: TestMessage[], public scheduler: Scheduler) {
     super();
-    this.scheduler = scheduler;
   }
 
   /** @internal */
   protected _subscribe(subscriber: Subscriber<any>): Subscription {
-    const subject: HotObservable<T> = this;
-    const index = subject.logSubscribedFrame();
+    const index = this.logSubscribedFrame();
     const subscription = new Subscription();
     subscription.add(
       new Subscription(() => {
-        subject.logUnsubscribedFrame(index);
+        this.logUnsubscribedFrame(index);
       })
     );
     subscription.add(super._subscribe(subscriber));
@@ -36,18 +31,10 @@ export class HotObservable<T> extends Subject<T> implements SubscriptionLoggable
   }
 
   setup() {
-    const subject = this;
-    const messagesLength = subject.messages.length;
-    /* tslint:disable:no-var-keyword */
-    for (let i = 0; i < messagesLength; i++) {
-      (() => {
-        const { notification, frame } = subject.messages[i];
-        /* tslint:enable */
-        subject.scheduler.schedule(() => {
-          observeNotification(notification, subject);
-        }, frame);
-      })();
+    for (const { notification, frame } of this.messages) {
+      this.scheduler.schedule(() => {
+        observeNotification(notification, this);
+      }, frame);
     }
   }
 }
-applyMixins(HotObservable, [SubscriptionLoggable]);
diff --git a/src/internal/testing/SubscriptionLog.ts b/src/internal/testing/SubscriptionLog.ts
deleted file mode 100644
index 367a6d9691..0000000000
--- a/src/internal/testing/SubscriptionLog.ts
+++ /dev/null
@@ -1,5 +0,0 @@
-export class SubscriptionLog {
-  constructor(public subscribedFrame: number,
-              public unsubscribedFrame: number = Infinity) {
-  }
-}
\ No newline at end of file
diff --git a/src/internal/testing/SubscriptionLoggable.ts b/src/internal/testing/SubscriptionLoggable.ts
deleted file mode 100644
index e8def0419f..0000000000
--- a/src/internal/testing/SubscriptionLoggable.ts
+++ /dev/null
@@ -1,22 +0,0 @@
-import { Scheduler } from '../Scheduler';
-import { SubscriptionLog } from './SubscriptionLog';
-
-export class SubscriptionLoggable {
-  public subscriptions: SubscriptionLog[] = [];
-  // @ts-ignore: Property has no initializer and is not definitely assigned
-  scheduler: Scheduler;
-
-  logSubscribedFrame(): number {
-    this.subscriptions.push(new SubscriptionLog(this.scheduler.now()));
-    return this.subscriptions.length - 1;
-  }
-
-  logUnsubscribedFrame(index: number) {
-    const subscriptionLogs = this.subscriptions;
-    const oldSubscriptionLog = subscriptionLogs[index];
-    subscriptionLogs[index] = new SubscriptionLog(
-      oldSubscriptionLog.subscribedFrame,
-      this.scheduler.now()
-    );
-  }
-}
diff --git a/src/internal/testing/TestScheduler.ts b/src/internal/testing/TestScheduler.ts
index 0045166740..f4ad50d796 100644
--- a/src/internal/testing/TestScheduler.ts
+++ b/src/internal/testing/TestScheduler.ts
@@ -2,7 +2,7 @@ import { Observable } from '../Observable';
 import { ColdObservable } from './ColdObservable';
 import { HotObservable } from './HotObservable';
 import { TestMessage } from './TestMessage';
-import { SubscriptionLog } from './SubscriptionLog';
+import { SubscriptionLog } from './subscription-logging';
 import { Subscription } from '../Subscription';
 import { VirtualTimeScheduler, VirtualAction } from '../scheduler/VirtualTimeScheduler';
 import { ObservableNotification } from '../types';
diff --git a/src/internal/testing/subscription-logging.ts b/src/internal/testing/subscription-logging.ts
new file mode 100644
index 0000000000..6f05905e60
--- /dev/null
+++ b/src/internal/testing/subscription-logging.ts
@@ -0,0 +1,19 @@
+interface SubscriptionLoggingProps {
+  subscriptions: SubscriptionLog[];
+  scheduler: { now(): number };
+}
+
+export class SubscriptionLog {
+  constructor(public subscribedFrame: number, public unsubscribedFrame: number = Infinity) {}
+}
+
+export function logUnsubscribedFrame(this: SubscriptionLoggingProps, index: number) {
+  const subscriptionLogs = this.subscriptions;
+  const oldSubscriptionLog = subscriptionLogs[index];
+  subscriptionLogs[index] = new SubscriptionLog(oldSubscriptionLog.subscribedFrame, this.scheduler.now());
+}
+
+export function logSubscribedFrame(this: SubscriptionLoggingProps): number {
+  this.subscriptions.push(new SubscriptionLog(this.scheduler.now()));
+  return this.subscriptions.length - 1;
+}
diff --git a/src/internal/util/applyMixins.ts b/src/internal/util/applyMixins.ts
deleted file mode 100644
index 7c1ed24232..0000000000
--- a/src/internal/util/applyMixins.ts
+++ /dev/null
@@ -1,10 +0,0 @@
-export function applyMixins(derivedCtor: any, baseCtors: any[]) {
-  for (let i = 0, len = baseCtors.length; i < len; i++) {
-    const baseCtor = baseCtors[i];
-    const propertyKeys = Object.getOwnPropertyNames(baseCtor.prototype);
-    for (let j = 0, len2 = propertyKeys.length; j < len2; j++) {
-      const name = propertyKeys[j];
-      derivedCtor.prototype[name] = baseCtor.prototype[name];
-    }
-  }
-}
\ No newline at end of file