How to share test cases in multiple suites with Jest?

Question

I found that I have many repeated tests cases in multiple integration tests in a Node.js REST API. So for example, I test invalid requests for every endpoint where I expect an error to always have the same properties.

import { app } from 'server';
import * as request from 'supertest';

describe('Authentication tests', () => {
    describe('POST /login', () => {
        // other test cases
        // describe('valid request should ...', () => {...})

        describe('invalid requests with missing fields', () => {
            let response = null;

            beforeAll(async () => {
                await request(app)
                    .post('/login')
                    .expect('Content-Type', 'application/json; charset=utf-8')
                    .field('email', 'invalid@test.com')
                    .then(res => {
                        response = res;
                    });
            });

            it('should return an invalid status code', () => {
                expect(response.status).toBe(400);
            });

            it('should return a valid error schema', () => {
                expect(typeof response.body).toBe('object');
                expect(response.body).toHaveProperty('error');
                expect(response.body.error).toHaveProperty('code');
                expect(response.body.error).toHaveProperty('message');
            });

            it('should return an error with explicit message', () => {
                expect(response.body.error).toHaveProperty('message');
            });
        });
    });
});

Does Jest provide any way to create some share tests so I can encapsulate this error validation and declare it in other suite cases avoiding so much repetition?

Answer 1

You can encapsulate these tests into a function. The docs says:

Tests must be defined synchronously for Jest to be able to collect your tests.

For example:

function createInvalidRequestTests() {
  describe('invalid request', () => {
    let response;
    beforeAll(async () => {
      // simulate request of supertest
      response = await Promise.resolve({ status: 400, body: { error: { code: 1, message: 'network error' } } });
    });

    it('should return an invalid status code', () => {
      expect(response.status).toBe(400);
    });

    it('should return a valid error schema', () => {
      expect(typeof response.body).toBe('object');
      expect(response.body).toHaveProperty('error');
      expect(response.body.error).toHaveProperty('code');
      expect(response.body.error).toHaveProperty('message');
    });

    it('should return an error with explicit message', () => {
      expect(response.body.error).toHaveProperty('message');
    });
  });
}

Then, you can use this function to define your tests. Jest test runner will collect and run these tests as usual

describe('Authentication tests', () => {
  describe('POST /login', () => {
    describe('valid request', () => {
      it('should login correctly', () => {
        expect(1).toBe(1);
      });
    });

    createInvalidRequestTests();
  });

  describe('POST /register', () => {
    describe('valid request', () => {
      it('should register correctly', () => {
        expect(2).toBe(2);
      });
    });

    createInvalidRequestTests();
  });
});

Unit test result:

 PASS  src/stackoverflow/58081822/index.spec.ts (9.622s)
  Authentication tests
    POST /login
      valid request
        ✓ should login correctly (5ms)
      invalid request
        ✓ should return an invalid status code
        ✓ should return a valid error schema (2ms)
        ✓ should return an error with explicit message
    POST /register
      valid request
        ✓ should register correctly (1ms)
      invalid request
        ✓ should return an invalid status code (1ms)
        ✓ should return a valid error schema (2ms)
        ✓ should return an error with explicit message (1ms)

Test Suites: 1 passed, 1 total
Tests:       8 passed, 8 total
Snapshots:   0 total
Time:        12.053s, estimated 14s