Angular Testing Guide

Write tests using Vitest with Angular TestBed following project patterns.

Note: Vitest globals (describe, it, expect, vi, beforeEach, afterEach) are pre-configured in tsconfig.spec.json - no imports needed.

Test File Location

Place test files next to the source files:

component-name/
  component-name.ts
  component-name.spec.ts  # <- Test file here

Essential Imports

import { ComponentFixture, TestBed } from "@angular/core/testing";
import { provideZonelessChangeDetection } from "@angular/core";
import { By } from "@angular/platform-browser";
// Vitest globals (describe, it, expect, vi) are available without imports

Component Test Template

import { ComponentFixture, TestBed } from "@angular/core/testing";
import { provideZonelessChangeDetection } from "@angular/core";
import { By } from "@angular/platform-browser";

import { MyComponent } from "./my";
import { MyService } from "../services/my";

describe("MyComponent", () => {
  let component: MyComponent;
  let fixture: ComponentFixture<MyComponent>;
  let mockService: Partial<MyService>;

  beforeEach(async () => {
    mockService = {
      getData: vi.fn(),
      saveData: vi.fn(),
    };

    await TestBed.configureTestingModule({
      imports: [MyComponent],
      providers: [
        provideZonelessChangeDetection(),
        { provide: MyService, useValue: mockService },
      ],
    }).compileComponents();

    fixture = TestBed.createComponent(MyComponent);
    component = fixture.componentInstance;
  });

  it("should create", () => {
    expect(component).toBeTruthy();
  });

  it("should render data when loaded", () => {
    // Arrange
    vi.mocked(mockService.getData).mockReturnValue(["item1", "item2"]);

    // Act
    fixture.detectChanges();

    // Assert
    const items = fixture.debugElement.queryAll(By.css(".item"));
    expect(items).toHaveLength(2);
  });

  it("should call service on button click", () => {
    // Arrange
    fixture.detectChanges();
    const button = fixture.debugElement.query(By.css("button"));

    // Act
    button.triggerEventHandler("click", null);

    // Assert
    expect(mockService.saveData).toHaveBeenCalled();
  });
});

Service Test Template

import { TestBed } from "@angular/core/testing";
import { provideZonelessChangeDetection } from "@angular/core";
import { provideHttpClient } from "@angular/common/http";
import {
  provideHttpClientTesting,
  HttpTestingController,
} from "@angular/common/http/testing";

import { MyService } from "./my";

describe("MyService", () => {
  let service: MyService;
  let httpMock: HttpTestingController;

  beforeEach(() => {
    TestBed.configureTestingModule({
      providers: [
        MyService,
        provideZonelessChangeDetection(),
        provideHttpClient(),
        provideHttpClientTesting(),
      ],
    });

    service = TestBed.inject(MyService);
    httpMock = TestBed.inject(HttpTestingController);
  });

  afterEach(() => {
    httpMock.verify();
  });

  it("should be created", () => {
    expect(service).toBeTruthy();
  });

  it("should fetch data from API", () => {
    // Arrange
    const mockData = [{ id: 1, name: "Test" }];

    // Act
    service.getData().subscribe((data) => {
      // Assert
      expect(data).toEqual(mockData);
    });

    // Assert HTTP request
    const req = httpMock.expectOne("/api/data");
    expect(req.request.method).toBe("GET");
    req.flush(mockData);
  });
});

Testing Signal Inputs

import { signal } from "@angular/core";

it("should respond to input changes", () => {
  // For required inputs, set before detectChanges
  fixture.componentRef.setInput("data", { id: 1, name: "Test" });
  fixture.detectChanges();

  expect(component.data()).toEqual({ id: 1, name: "Test" });
});

Testing Outputs

it("should emit event on action", () => {
  const emitSpy = vi.fn();
  component.valueChange.subscribe(emitSpy);

  component.updateValue(42);

  expect(emitSpy).toHaveBeenCalledWith(42);
});

Mocking Patterns

// Mock service methods
const mockService = {
  getData: vi.fn().mockReturnValue(of(["data"])),
  saveData: vi.fn().mockResolvedValue({ success: true }),
};

// Spy on existing service
const service = TestBed.inject(MyService);
const spy = vi.spyOn(service, "getData").mockReturnValue(of(["mocked"]));

// Mock external module
vi.mock("external-lib", () => ({
  someFunction: vi.fn(() => "mocked result"),
}));

Async Testing

// Using async/await
it("should handle async operations", async () => {
  vi.mocked(mockService.getData).mockResolvedValue(["async data"]);

  await component.loadData();
  fixture.detectChanges();

  expect(component.items()).toEqual(["async data"]);
});

// Testing Observables
it("should handle observable", () => {
  vi.mocked(mockService.getData).mockReturnValue(of(["data"]));

  service.getData().subscribe((result) => {
    expect(result).toEqual(["data"]);
  });
});

Fake Timers

it("should handle delayed operations", () => {
  vi.useFakeTimers();

  component.startTimer();
  vi.advanceTimersByTime(1000);

  expect(component.timerComplete()).toBe(true);

  vi.useRealTimers();
});

DOM Queries

// Query by CSS selector
const element = fixture.debugElement.query(By.css(".my-class"));
const elements = fixture.debugElement.queryAll(By.css("button"));

// Query by directive
const directive = fixture.debugElement.query(By.directive(MyDirective));

// Get native element
const nativeElement = element.nativeElement;
expect(nativeElement.textContent).toContain("Expected text");

Checklist

• Vitest globals available (no imports needed)
• Using provideZonelessChangeDetection() in providers
• Following AAA pattern (Arrange, Act, Assert)
• Mocking external dependencies
• Testing component inputs and outputs
• Verifying HTTP requests with httpMock.verify()
• Using descriptive test names