Create test_total_bill.py

[dhyanikindasus]

This PR improves the Total_Bill() method in the café management system by:

Using a price dictionary to reduce repetitive code.

Simplifying cost calculations and GUI updates.

Adding error handling for invalid or empty inputs.

Renaming variables to avoid conflicts and improve clarity.

These changes make the billing logic cleaner, safer, and easier to maintain.

PR Title Refactor: Improve Total_Bill() logic and add error handling

Summary This PR refactors the Total_Bill() method in the café management system for better structure, reliability, and clarity.

Description The existing billing logic was functional but repetitive and prone to input errors. This PR introduces structured improvements to enhance readability and maintainability.

The changes are as follows: Used a price dictionary to eliminate repetitive price declarations.

Simplified item cost and total bill calculations using loops and conditionals.

Added input validation and error handling for non-numeric and empty values.

Cleaned up GUI entry field updates to prevent value stacking.

Improved naming consistency for better readability.

Checks In the repository Made no changes that degrade the functioning of the repository

Gave each commit a meaningful title

In the PR Followed the format of the pull_request_template

Kept the PR focused and well-scoped

Tested the changes locally

Thank You, Dhyani Upadhyay @dhyanikindasus