Angular Unit Testing

Angular Unit Testing

Setup

• Use Jest as the test runner (npm test, npm run test:ci).
• Angular integration is provided by jest-preset-angular; the setup file is src/testing/setup.ts.
• Jest globals (describe, it, expect, jest, beforeEach, etc.) are available without imports — do not import them; they are injected automatically.

File conventions

• Test files live next to the file under test: foo.service.spec.ts alongside foo.service.ts.
• One spec file per source file.
• Test match pattern: src/app/**/*.spec.ts.

Test structure

import { TestBed } from '@angular/core/testing';
import { MyService } from './my.service';
import { SomeDependency } from './some.dependency';

const buildMocks = () => ({
    someDependency: { getData: jest.fn().mockReturnValue(of('result')) } as unknown as SomeDependency
});

let service: MyService;
let mocks: ReturnType<typeof buildMocks>;

beforeEach(() => {
    mocks = buildMocks();
    TestBed.configureTestingModule({
        providers: [
            MyService,
            { provide: SomeDependency, useValue: mocks.someDependency }
        ]
    });
    service = TestBed.inject(MyService);
});

describe('MyService', () => {
    describe('myMethod', () => {
        it('should return expected result', () => { /* ... */ });
    });
});

• Always call TestBed.configureTestingModule in beforeEach — Angular resets TestBed between tests automatically.
• Build mocks with buildMocks() factory in beforeEach — never share mutable mock state across tests.

Mocking modules and classes

Use jest.mock(...) at the top of the file, then override behaviour in beforeEach:

jest.mock('./auth.service');
jest.mock('../services/current-user.service');

const loginMock = jest.fn().mockReturnValue(Promise.resolve());

const mockServicesWith = (user: UserProfile | null) => {
    mockClass(AuthService, () => Object({
        isAuthenticated: () => user !== undefined,
        loginRedirect: loginMock
    }));
};

beforeEach(() => {
    loginMock.mockClear();
    TestBed.configureTestingModule({ providers: [AuthService] });
});

Use the mockClass helper from @test/mocks/class-mocker to configure mock constructors:

import { mockClass } from '@test/mocks/class-mocker';

mockClass(CurrentUserService, () => Object({ currentUser: () => user }));

HTTP interceptor testing

For interceptor tests, use AngularTesterBuilder from @test/builders/angular-tester-builder:

import { AngularTester, AngularTesterBuilder } from '@test/builders/angular-tester-builder';

let tester: AngularTester;

beforeEach(async() => {
    tester = await new AngularTesterBuilder()
        .withProviders([
            provideHttpClient(withInterceptors([myInterceptor])),
            provideHttpClientTesting(),
            { provide: MyService, useFactory: mockMyService }
        ])
        .build();
});

it('should add header to API requests', (done: jest.DoneCallback) => {
    tester.requestSuccess(done, (result: TestRequest) => {
        expect(result.request.headers.get('X-Custom')).toEqual('value');
    });
});

Parameterized tests — describe.each / it.each

Always scan for duplication before writing a new it(). If multiple tests share the same body and differ only in input values, collapse them with describe.each or it.each:

// ❌ avoid — identical structure, only data differs
it('should forbid null user', () => { ... });
it('should forbid user without permission', () => { ... });
it('should allow user with permission', () => { ... });

// ✅ correct — one parameterized block
describe.each([
    { description: 'should forbid null user', user: null, allowed: false },
    { description: 'should forbid user without permission', user: userWithoutPerm, allowed: false },
    { description: 'should allow user with permission', user: userWithPerm, allowed: true }
])('PermissionService', ({ description, user, allowed }) => {
    it(description, () => {
        const service = arrangeWith(user);
        expect(service.hasPermissions([PermissionId.ProductsWrite])).toBe(allowed);
    });
});

Async tests

• Always await async service calls; never use void or fire-and-forget in tests.
• Use (done: jest.DoneCallback) for callback-style async (e.g. HTTP mock assertions):

it('should resolve with data', async() => {
    await expect(service.loadData()).resolves.toEqual({ id: 1 });
});

Pure function testing (no Angular)

For utilities and pure functions, skip TestBed entirely:

import { myUtil } from './my-util';

describe('myUtil', () => {
    it('should transform input correctly', () => {
        const result = myUtil('input');
        expect(result).toBe('expected');
    });
});

Coverage

• Run npm run test:ci to generate coverage.
• Coverage is collected from src/app/core/**, src/app/shared/models/**, src/app/shared/pipes/**, src/app/shared/services/**, src/app/shared/validators/**.
• Aim to cover all public methods and the primary happy/error paths.
• Do not write coverage-padding tests that add no semantic value.

What NOT to do

• Do not import describe, it, expect, or jest from any module — they are global.
• Do not use Jasmine, Karma, or Vitest — the project uses Jest with jest-preset-angular.
• Do not use .subscribe() in tests — use firstValueFrom() or pass of(value) directly.
• Do not share mutable mock state across tests — recreate mocks in beforeEach.
• Do not snapshot-test Angular services — snapshots are for component templates and complex output.
• Do not leave console.error unchecked; if a code path logs an error, assert jest.spyOn(console, 'error') was called.