Testing branch

[Gambit142]

This branch uses the jest framework for testing the CRUD functions used to make the todo-list app run successfully.

I created two mock files called localstorage.js to imitate the functions of the browser's localStorage and crud.js to mock the CRUD functions.

I created a __tests__ folder and put a crud.test.js file in it. The test file checks if the following operations are performed successfully:

• Mock HTML to test if add/delete functions add or remove exactly one
• element to/from the list in the DOM.
• create a function for editing the task description.
• create a function for updating an item's 'completed' status.
• create the "Clear all completed" function.

The tests for all the operations mentioned above were grouped in a description() method.