add unit tests

src/app/services/global-settings.service.spec.ts

@@ -1,16 +1,46 @@
 import {TestBed} from '@angular/core/testing';
-
+import {of} from 'rxjs';
+import {DbService} from './db.service';
 import {GlobalSettingsService} from './global-settings.service';
 
 describe('GlobalSettingsService', () => {
   let service: GlobalSettingsService;
+  let dbServiceSpy: jasmine.SpyObj<DbService>;
+  let updateSpy: jasmine.Spy;
 
   beforeEach(() => {
-    void TestBed.configureTestingModule({});
+    updateSpy = jasmine.createSpy('update').and.resolveTo();
+    dbServiceSpy = jasmine.createSpyObj<DbService>('DbService', ['doc$', 'doc']);
+    dbServiceSpy.doc$.and.returnValue(of({churchName: 'ICF'}) as never);
+    dbServiceSpy.doc.and.returnValue({update: updateSpy} as never);
+
+    void TestBed.configureTestingModule({
+      providers: [{provide: DbService, useValue: dbServiceSpy}],
+    });
+
     service = TestBed.inject(GlobalSettingsService);
   });
 
   it('should be created', () => {
-    void expect(service).toBeTruthy();
+    expect(service).toBeTruthy();
+  });
+
+  it('should read the static global settings document once on creation', () => {
+    expect(dbServiceSpy.doc$).toHaveBeenCalledTimes(1);
+    expect(dbServiceSpy.doc$).toHaveBeenCalledWith('global/static');
+  });
+
+  it('should expose the shared settings stream via the getter', done => {
+    service.get$.subscribe(settings => {
+      expect(settings).toEqual({churchName: 'ICF'} as never);
+      done();
+    });
+  });
+
+  it('should update the static global settings document', async () => {
+    await service.set({churchName: 'New Name'} as never);
+
+    expect(dbServiceSpy.doc).toHaveBeenCalledWith('global/static');
+    expect(updateSpy).toHaveBeenCalledWith({churchName: 'New Name'} as never);
   });
 });