Parallel Change Kata

Credits

Inspired by Pawel Duda & Carlos Ble

Your Task

Change the class ShoppingCart in the package field.

The class should be handle multiple int items instead of a single one.

Tests have already been written.

Rules

The tests must not be red at any time. No compile-errors, no failures.

Get the Code

On GitHub (This kata can be done using C++, C#, Go, Java, Python, Ruby) If your favorite language is missing, feel free to create a pull request. Be sure the maintainer will be happy ;-)