[Test Improvement] Check whether order total on the cart is correct

Problem/Motivation

As a foolproof test, verify whether the total appearing on the ajax cart is same as the order total obtained from the backend.

Proposed resolution

Update the tests. This can be done after #2930680: [Test Improvement] Check whether the product is gone from the backend also.

Remaining tasks

N/A

User interface changes

N/A

API changes

N/A

Data model changes

N/A