Writing Unit Test for Joi Schema Validation

I am using Joi Schema for Express Request Body Validation in one of my projects. So, I was writing Unit Test for Joi Schema middleware validation yesterday and I think it's good to document this down.

I created a sample Express project where we have a POST endpoint to create a journal for a book (where we journal down our learning for a book after we read it).

router.post('journal', bodyValidator(createJournalSchema), journalController.journal);

What's bodyValidator do?

Body Validator basically validate the req.body to ensure all the required fields is provided before we proceed.

// requestValidator.js /** * Validate body request * @param {Object} schema - Joi object schema */ const bodyValidator = (schema) => (req, res, next) => { const { error } = schema.validate(req.body); if (error) { const errorMessages = error.details.map((detail) => detail.message); return res.status(400).json({ error: errorMessages }); } return next(); };

Unit Testing for Joi Schema

According to the bodyValidator above, I designed 2 unit tests.

1. Expect Bad Request (statusCode 400) return when the validation failed.
2. Expect Next Middleware to be called if the validation passed.

test('Return 400 when the create journal schema validation is failed', () => { const req = mockRequest({ bookId: 1, }); const res = mockResponse(); const next = mockNext(); bodyValidator(createJournalSchema)(req, res, next); // Expect status 400 bad request called if there is error expect(res.status).toHaveBeenCalledWith(400); expect(res.json).toHaveBeenCalledTimes(1); expect(next).toHaveBeenCalledTimes(0); }); test('Next middleware is called when the create journal schema validation is successful', () => { const req = mockRequest({ bookId: 1, journal: 'This is the summary of my reading today...' }); const res = mockResponse(); const next = mockNext(); bodyValidator(createJournalSchema)(req, res, next); // Expect next middleware called if validation is passed expect(next).toHaveBeenCalled(); expect(next).toHaveBeenCalledTimes(1); });

In addition, you can also write more detailed unit tests where covered the invalid data type. For e.g, you can try changing bookId to '1' and expect validation failed which is not covered in this post.

Full source code can be found here.

Thanks for reading.