- Should be able to create a new user
- Should be able to list all user's todos
- Should be able to create a new todo
- Should be able to update a todo
- Should be able to mark a todo as done
- Should be able to delete a todo
- Should not be able to create a new user when username already exists
- Should not be able to update a non existing todo
- Should not be able to mark a non existing todo as done
- Should not be able to delete a non existing todo