add unit tests

src/app/services/config.service.spec.ts

@@ -1,16 +1,40 @@
 import {TestBed} from '@angular/core/testing';
-
+import {of} from 'rxjs';
+import {DbService} from './db.service';
 import {ConfigService} from './config.service';
 
 describe('ConfigService', () => {
   let service: ConfigService;
+  let dbServiceSpy: jasmine.SpyObj<DbService>;
 
   beforeEach(() => {
-    void TestBed.configureTestingModule({});
+    dbServiceSpy = jasmine.createSpyObj<DbService>('DbService', ['doc$']);
+    dbServiceSpy.doc$.and.returnValue(of({copyright: 'CCLI'}) as never);
+
+    void TestBed.configureTestingModule({
+      providers: [{provide: DbService, useValue: dbServiceSpy}],
+    });
+
     service = TestBed.inject(ConfigService);
   });
 
   it('should be created', () => {
-    void expect(service).toBeTruthy();
+    expect(service).toBeTruthy();
+  });
+
+  it('should read the global config document once on creation', () => {
+    expect(dbServiceSpy.doc$).toHaveBeenCalledTimes(1);
+    expect(dbServiceSpy.doc$).toHaveBeenCalledWith('global/config');
+  });
+
+  it('should expose the shared config stream via get$', done => {
+    service.get$().subscribe(config => {
+      expect(config).toEqual({copyright: 'CCLI'} as never);
+      done();
+    });
+  });
+
+  it('should resolve the current config via get()', async () => {
+    await expectAsync(service.get()).toBeResolvedTo({copyright: 'CCLI'} as never);
   });
 });