Unit testing middleware

Next, we are going to test our middleware functions, starting with the checkEmptyPayload middleware. Like we did previously, move the middleware module into its own directory:

$ cd src/middlewares/ && \
  mkdir check-empty-payload && \
  mv check-empty-payload.js check-empty-payload/index.js && \
  touch check-empty-payload/index.unit.test.js && \
  cd ../../

Then, inside src/middlewares/check-content-type.js/index.unit.test.js, lay out the skeleton of our first test:

import assert from 'assert';
import checkEmptyPayload from '.';

describe('checkEmptyPayload', function () {
  describe('When req.method is not one of POST, PATCH or PUT', function () {
    it('should not modify res', function () {
      // Assert that `res` has not been modified
    });

    it('should call next() once', function () {
      // Assert that `next` has been called once
    });
  });});

The purpose of the checkEmptyPayload middleware is to ensure that the POST...