Add service to store the app state

src/app/shared/services/store.service.spec.ts

+import { TestBed } from '@angular/core/testing';
+
+import { StoreService } from './store.service';
+
+describe('StoreService', () => {
+  let service: StoreService;
+
+  beforeEach(() => {
+    TestBed.configureTestingModule({
+      providers: [StoreService]
+    });
+    service = TestBed.inject(StoreService);
+  });
+
+  it('should be created', () => {
+    expect(service).toBeTruthy();
+  });
+});

src/app/shared/services/store.service.ts

+import { Injectable } from '@angular/core';
+
+@Injectable()
+export class StoreService {
+
+  constructor() { }
+}

src/app/shared/shared.module.ts

 import { NgModule } from '@angular/core';
 import { CommonModule } from '@angular/common';
 import { BackendService } from './services/backend.service';
+import { StoreService } from './services/store.service';
 
 @NgModule({
   declarations: [],
@@ -8,7 +9,8 @@ import { BackendService } from './services/backend.service';
     CommonModule
   ],
   providers: [
-    BackendService
+    BackendService,
+    StoreService,
   ]
 })
 export class SharedModule { }