Jest error: TypeError: Cannot read properties of undefined (reading 'send')

Question

I'm fairly new to jest testing and thought I'd write a simple test for one of my controls that simply sends an array of user objects, or a simple string statement if the array is empty. So this test should just pass the text "No users found".

Here is the simple test I wrote:

test('Should return a string statment *No users found*', () => {
    expect(getAllUsers().toBe('No users found'));
});

Not sure what I'm doing wrong here...

Here is the error I'm getting:

 TypeError: Cannot read properties of undefined (reading 'send')

       6 |
       7 | export const getAllUsers = (req, res) => {
    >  8 |     if(users.length === 0) res.send('No users found');
         |                                ^
       9 |     res.send(users);
      10 | };
      11 |

Answer 1

TypeError: Cannot read properties of undefined (reading 'send')

It is because there is no res object in the getAllUsers function. You need to create a mock response and request and pass it to the function.

const sinon = require('sinon');

const mockRequest = () => {
  return {
    users: [];
  };
};

const mockResponse = () => {
  const res = {};
  res.status = sinon.stub().returns(res);
  res.json = sinon.stub().returns(res);
  return res;
};

describe('checkAuth', () => {
  test('should 401 if session data is not set', async () => {
    const req = mockRequest();
    const res = mockResponse();
    await getAllUsers(req, res);
    expect(res.status).toHaveBeenCalledWith(404);
  });
});

Note: You need to check this URL to actually understand how we should test the express API with Jest.

In the function, where are you reading users ? As the response is dependent on users so make sure you pass it to the method while testing it.