[ADF-4364] Fix Back button action on Viewer Component (#4613)

* [ADF-3364] Fix Back button action on Viewer Component

* [ADF-4364] Fix Module providers

* [ADF-4364] Add unit tests

* [ADF-4364] Fix unit tests

* [ADF-4364] Fix lazy loading module of Viewer component

lib/core/services/previous-route.service.spec.ts

@@ -0,0 +1,61 @@
+/*!
+ * @license
+ * Copyright 2019 Alfresco Software, Ltd.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { TestBed } from '@angular/core/testing';
+import { setupTestBed } from '../testing/setupTestBed';
+import { PreviousRouteService } from './previous-route.service';
+import { Router, NavigationEnd } from '@angular/router';
+import { Observable } from 'rxjs';
+import { CoreTestingModule } from 'core/testing/core.testing.module';
+
+class MockRouter {
+    firstUrl = new NavigationEnd(0, '/files', '/files');
+    secondUrl = new NavigationEnd(0, '/home', '/home');
+    events = new Observable((observer) => {
+        observer.next(this.firstUrl);
+        observer.next(this.secondUrl);
+        observer.complete();
+    });
+}
+
+describe('Previous route service ', () => {
+
+    let previousRouteService: PreviousRouteService;
+
+    setupTestBed({
+        imports: [
+            CoreTestingModule
+        ],
+        providers: [
+            { provide: Router, useClass: MockRouter },
+            PreviousRouteService
+        ]
+    });
+
+    beforeEach(() => {
+        previousRouteService = TestBed.get(PreviousRouteService);
+    });
+
+    it('should be able to create the service', () => {
+        expect(previousRouteService).not.toBeNull();
+        expect(previousRouteService).toBeDefined();
+    });
+
+    it('should set curent url when new page loads', () => {
+        expect(previousRouteService.getPreviousUrl()).toBe('/files');
+    });
+});