Add getInstanceWithProviders() utility for testing services with dependencies

projects/testing-library/src/lib/testing-library.ts

@@ -42,6 +42,14 @@ type SubscribedOutput<T> = readonly [key: keyof T, callback: (v: any) => void, s
 const mountedFixtures = new Set<ComponentFixture<any>>();
 const safeInject = TestBed.inject || TestBed.get;
 
+export function getInstanceWithProviders<T>(serviceClass: Type<T>, providers: any[]): T {
+  TestBed.configureTestingModule({
+    providers: [serviceClass, ...providers],
+  });
+
+  return TestBed.inject(serviceClass);
+}
+
 export async function render<ComponentType>(
   component: Type<ComponentType>,
   renderOptions?: RenderComponentOptions<ComponentType>,

projects/testing-library/tests/getInstanceWithProviders.spec.ts

@@ -0,0 +1,28 @@
+import { Injectable } from '@angular/core';
+import { getInstanceWithProviders } from '../src/lib/testing-library';
+
+describe('getInstanceWithProviders', () => {
+  @Injectable()
+  class DatabaseService {
+    getData() {
+      return 'real data';
+    }
+  }
+
+  @Injectable()
+  class UserService {
+    constructor(private db: DatabaseService) {}
+
+    getUser() {
+      return `User: ${this.db.getData()}`;
+    }
+  }
+
+  it('should inject a mock service into a service that depends on it', () => {
+    const mockDatabase = { getData: () => 'mock data' };
+
+    const userService = getInstanceWithProviders(UserService, [{ provide: DatabaseService, useValue: mockDatabase }]);
+
+    expect(userService.getUser()).toBe('User: mock data');
+  });
+});