When you finally create the real data/function, do you remove the stubs/mock/fake data afterwards?

Hello

You use the same function for both your test and your mockdata, you just import/require that function into the test folder to use it.

Ill use your example above:

// ./main.js - you actual file

function functionOne (para1) {
    return para1;
};


// .main.spec.js - your test file

describe('A suite is just a function', function() {

    // Before each spec we want to require the file we are testing
    beforeEach(function() {
        const component = require('./main.js');
    });

    // Within the test we get the main.js function from the actual file
    it("and so is a spec", function() {
      expect(component.functionOne(2)).to.equal(2);
    });
  });

As you can see i want to test the actual function but we provide "mock data" by the number of 2 to see if the actual function returns the correct value.

Hope this helps!

Hello

You should always keep your mock data, this should also always simulate your real data. Its good for keeping a history of what you tested.

This is just used to test functionality without making costly requests to real data.

For example: lets say a snippet of your real database looked like this, you want to copy that and test it works as intended with mock data

[
{
   "id": "0001",
   "name": "John Doe",
},
{
   "id": "0002",
   "name": "Jane Doe",
}
]

You want to simulate the real database with your mock one but as far as your test is concerned, you just care about what data is returned, your test is just ensuring the functionality happens.

So a test for a function

getsUserById(0002); // return 1 object from the mock data

Our test would check the functionality works to return 1 user with that same ID.

Or maybe you want to test that it will return an error when a ID doesn't exist:

getUserById(1234); // return error

So your tests are just a way of you using some data without using the real thing, allowing you to test any outcome whether that is a good request, 400 bad request, 401 unauthorized, 404 not found, 408 timeout... the list goes on and you can change the mock data to test each and every outcome.