added test and docs for 404 operator

src/app/core/shared/operators.spec.ts

@@ -13,9 +13,11 @@ import {
   getRequestFromRequestUUID,
   getResourceLinksFromResponse,
   getResponseFromEntry,
-  getSucceededRemoteData
+  getSucceededRemoteData, redirectToPageNotFoundOn404
 } from './operators';
 import { RemoteData } from '../data/remote-data';
+import { RemoteDataError } from '../data/remote-data-error';
+import { of as observableOf } from 'rxjs';
 
 describe('Core Module - RxJS Operators', () => {
   let scheduler: TestScheduler;
@@ -193,6 +195,34 @@ describe('Core Module - RxJS Operators', () => {
     });
   });
 
+  describe('redirectToPageNotFoundOn404', () => {
+    let router;
+    beforeEach(() => {
+      router = jasmine.createSpyObj('router', ['navigateByUrl']);
+    });
+
+    it('should call navigateByUrl to a 404 page, when the remote data contains a 404 error', () => {
+      const testRD = new RemoteData(false, false, false, new RemoteDataError(404, 'Not Found', 'Object was not found'), undefined);
+
+      observableOf(testRD).pipe(redirectToPageNotFoundOn404(router)).subscribe();
+      expect(router.navigateByUrl).toHaveBeenCalledWith('/404', { skipLocationChange: true });
+    });
+
+    it('should not call navigateByUrl to a 404 page, when the remote data contains another error than a 404', () => {
+      const testRD = new RemoteData(false, false, false, new RemoteDataError(500, 'Server Error', 'Something went wrong'), undefined);
+
+      observableOf(testRD).pipe(redirectToPageNotFoundOn404(router)).subscribe();
+      expect(router.navigateByUrl).not.toHaveBeenCalled();
+    });
+
+    it('should not call navigateByUrl to a 404 page, when the remote data contains no error', () => {
+      const testRD = new RemoteData(false, false, true, null, undefined);
+
+      observableOf(testRD).pipe(redirectToPageNotFoundOn404(router)).subscribe();
+      expect(router.navigateByUrl).not.toHaveBeenCalled();
+    });
+  });
+
   describe('getResponseFromEntry', () => {
     it('should return the response for all not empty request entries, when they have a value', () => {
       const source = hot('abcdefg', testRCEs);