Use spy objects.

src/app/app.component.spec.ts

@@ -4,32 +4,22 @@ import {FormsModule} from '@angular/forms';
 import {InputComponentManagerService} from './input-component-manager.service';
 import {Step} from './step';
 import {ConverterRegistryService} from './converter-registry.service';
-import {Converter} from './converter/converter';
 import {VersionComponent} from './version/version.component';
+import createSpyObj = jasmine.createSpyObj;
 
 describe('AppComponent', () => {
   let sut: AppComponent;
   let fixture: ComponentFixture<AppComponent>;
   const firstStep: Step = new Step(0);
 
-  const inputComponentManagerServiceStub = {
-    getFirst: () => {
-      return firstStep;
-    }
-  };
+  const inputComponentManagerServiceStub = createSpyObj(['getFirst']);
+  inputComponentManagerServiceStub.getFirst.and.returnValue(firstStep);
 
-  const converterRegistryServiceStub = {
-    getAllConverters: (): Converter[] => {
-      return [];
-    },
-
-    getConverter: (id: string): Converter => {
-      return undefined;
-    }
-  };
+  const converterRegistryServiceStub = createSpyObj(['getAllConverters', 'getConverter']);
+  converterRegistryServiceStub.getAllConverters.and.returnValue([]);
+  converterRegistryServiceStub.getConverter.and.returnValue(undefined);
 
   beforeEach(async(() => {
-    /*return */
     TestBed.configureTestingModule({
       declarations: [AppComponent, VersionComponent],
       imports: [FormsModule],