Refactored InvoiceService | Removed Repetitive Code | Created Interface & Private Methods | Added Caching | Added Mock Unit Tests

[RubyM77777]

… for clear readability & flexible to add new Constants.

2.Added NULL & Zero Invoice checks to avoid Exceptions & to achieve Test coverage. 3.Reduce Nested IfElse to avoid confusion and improve readability 4.Repeated calculations are stored in seperate variables to reduce DB calls & improve Page Performance 5.Created private method to Calculate the payment & save the invoice (Removed repetitive code & calculations). 6.Clear variable & method names for better understanding. 7.Used repository to save instead of direct DB save (inv.Save()). 8.Added Cache to store the invoice & to avoid multiple DB calls for the same invoice reference. 9.Installed Moq & added Unit Tests. Achived Test Coverage (Positive/Negative/NULL/Empty/EdgeCase Scenarios) & all Unit Tests Passed.

[RubyM77777]

Made below changes:

1. Moved all the hardcoded Response Messages & Rates into new classes for clear readability & flexible to add new Constants.
   2.Added NULL & Zero Invoice checks to avoid Exceptions & to achieve Test coverage.
   3.Reduce Nested IfElse to avoid confusion and improve readability
   4.Repeated calculations are stored in seperate variables to reduce DB calls & improve Page Performance
   5.Created private method to Calculate the payment & save the invoice (Removed repetitive code & calculations).
   6.Clear variable & method names for better understanding.
   7.Used repository to save instead of direct DB save (inv.Save()).
   8.Added Cache to store the invoice & to avoid multiple DB calls for the same invoice reference.
   9.Installed Moq & added Unit Tests. Achived Test Coverage (Positive/Negative/NULL/Empty/EdgeCase Scenarios) & all Unit Tests Passed.