Add unit tests for Bank Reconciliation Tool

[barredterra]

Test cases:

• [x] reconcile a bank transaction with a payment voucher
• [x] reconcile a bank transaction with multiple payment vouchers
• [x] reconcile multiple bank transactions with a payment voucher
• [x] reconcile a bank transaction with an unpaid invoice
• [x] reconcile a bank transaction with multiple unpaid invoices
• [x] reconcile multiple bank transactions with an unpaid invoice
• [x] reconcile a bank transaction by creating a payment entry
• [x] reconcile a bank transaction by creating a journal entry
• [x] partially reconcile a bank transaction with an unpaid invoice and create a journal entry for the remaining amount
• [ ] partially reconcile a bank transaction with an unpaid invoice and create a payment entry for the remaining amount