add unit tests

src/app/modules/songs/services/file.service.spec.ts

@@ -1,23 +1,45 @@
 import {TestBed} from '@angular/core/testing';
 import {Storage} from '@angular/fire/storage';
-
-import {FileService} from './file.service';
 import {FileDataService} from './file-data.service';
+import {FileService} from './file.service';
 
 describe('FileService', () => {
   let service: FileService;
+  let fileDataServiceSpy: jasmine.SpyObj<FileDataService>;
 
   beforeEach(() => {
+    fileDataServiceSpy = jasmine.createSpyObj<FileDataService>('FileDataService', ['delete']);
+    fileDataServiceSpy.delete.and.resolveTo();
+
     void TestBed.configureTestingModule({
       providers: [
-        {provide: Storage, useValue: {}},
-        {provide: FileDataService, useValue: {delete: () => Promise.resolve()}},
+        {provide: Storage, useValue: {app: 'test-storage'}},
+        {provide: FileDataService, useValue: fileDataServiceSpy},
       ],
     });
+
     service = TestBed.inject(FileService);
   });
 
   it('should be created', () => {
-    void expect(service).toBeTruthy();
+    expect(service).toBeTruthy();
+  });
+
+  it('should resolve download urls via AngularFire storage helpers', async () => {
+    const resolveSpy = spyOn<any>(service, 'resolveDownloadUrl').and.resolveTo('https://cdn.example/file.pdf');
+
+    await expectAsync(service.getDownloadUrl('songs/song-1/file.pdf').toPromise()).toBeResolvedTo('https://cdn.example/file.pdf');
+
+    expect(resolveSpy).toHaveBeenCalledWith('songs/song-1/file.pdf');
+  });
+
+  it('should delete the file from storage and metadata from firestore', async () => {
+    const deleteFromStorageSpy = spyOn<any>(service, 'deleteFromStorage').and.resolveTo();
+
+    service.delete('songs/song-1/file.pdf', 'song-1', 'file-1');
+    await Promise.resolve();
+
+    expect(deleteFromStorageSpy).toHaveBeenCalledWith('songs/song-1/file.pdf');
+    expect(fileDataServiceSpy.delete).toHaveBeenCalledWith('song-1', 'file-1');
   });
 });