Straight to the point

What do we mean by API Testing?

Test Data flow / DB Queries
Test input/output data transform
Test CRUD operations
Test REST Endpoints
Test Authentication

What is Usual approach to test this?

Integration Tests

Test the whole module
Test Service
Mock dependencies

Update Mock dependencies

Update Mock dependencies

Update Mock dependencies

Test REST API

Mock Authentication
Mock Database / Data Repository
Mock all functions returning data

jest.mock('../../../api/src/user/user.service', () => ({...}));
jest.mock('../../../api/src/color/color.service', () => ({...}));
jest.mock('../../../api/src/record/record.service', () => ({...}));
jest.mock('../../../api/src/track/track.service', () => ({...}));
...

Change function -> new output / arguments

-> fix test

const updateSpy = jest.spyOn(projectService, 'update')
	.mockImplementation(async () => expectedResult as unknown as ProjectDto);

Is there alternative?

based on NestJS framework

// step #1 - initialize API

let app: INestApplication;
beforeAll(async () => {
    const moduleRef = await Test.createTestingModule({
        imports: [AppModule],
    })
        .overrideGuard(AuthGuard)
        .useClass(AuthGuardMock)
        .compile();

    app = moduleRef.createNestApplication();
    await app.init();
});

afterAll(async () => {
    await app.close();
});

e2e Tests for API

based on NestJS framework

// step #2 - mock authentication

class AuthGuardMock implements CanActivate {
    canActivate(context: ExecutionContext): boolean {
        const request = context.switchToHttp().getRequest();
        request.user = testUsers[0];
        return true;
    }
}

e2e Tests for API

based on NestJS framework

// step #3 - call API and test

await request(app.getHttpServer())
	.post(`/projects/${testProject.id}/tasks`)
	.send({
		details: 'test task text',
		userId: testId,
		dueDate: testDueDate,
	})
	.expect(201);

e2e Tests for API

based on NestJS framework

// step #4 - verify data

await request(app.getHttpServer())
        .get(`/project/${testProject.id}`)
        .send()
        .expect(200)
        .expect((res: Response) => {
            const data: ProjectDto = res.body;

            expect(data.id).toBe(testProject.id);
            ...
        });

e2e Tests for API

Pros

Easy to fix / no need to fix tests
Easy to modify
Test the whole workflow
The minimal amount of mocks
Usually tests are very readable

Cons

Can take time to write data creation code
Takes time to run tests (API initialization)
Need to prepare a minimal database (including one for CI server)

Date.now = (): number => {
        return 1635792963551;
    };

Special trick

const mockGlobalDate = (): Date => {
    const dateMock = new Date(1635792963551);

    global.Date = class DateMock extends Date {
        constructor(...args: any[]) {
            if (args.length) {
                // @ts-ignore
                super(...args);
            } else {
                super(dateMock.getTime());
            }
        }
    } as any;

    Date.now = (): number => {
        return dateMock.getTime();
    };
};

@ValentinKononov

https://slides.com/valentinkononov/e2e-api-test-nestjs

http://www.kononov.space

@ValentinKononov

Conclusion

Make coding easier - add tests
e2e tests make changes faster
e2e tests cover the whole flow
less mocks
more happiness