The best evidence to determine whether transactions have been executed by authorized employees is audit trails. Audit trails are secure records that catalog events or procedures to provide support documentation. They are used to authenticate security and operational actions, mitigate challenges, or provide proof of compliance and operational integrity2. Audit trails can track and trace the following information related to transactions:
Who initiated, approved, modified, or deleted a transaction
When a transaction occurred (date and time)
Where a transaction took place (location or device)
What type of transaction was performed (action or operation)
Why a transaction was executed (purpose or reason)
By analyzing audit trails, an IS auditor can verify whether transactions have been executed by authorized employees or not. Audit trails can also identify any unauthorized, fraudulent, or erroneous transactions that may have occurred. Audit trails can also help to resolve any disputes or discrepancies that may arise from transactions.
References:
What Is an Audit Trail? Everything You Need to Know

The best testing approach to facilitate rapid identification of application interface errors is automated testing.
Automated testing is the use of software tools or scripts to execute predefined test cases, compare expected and actual outcomes, and report any discrepancies. Automated testing can help to speed up the testing process, increase test coverage, reduce human errors, and improve test accuracy and consistency. Automated testing can also help to detect interface errors that may occur due to incompatible data formats, communication protocols, or system configurations. References:
* CISA Review Manual (Digital Version), Chapter 3, Section 3.3.11
* CISA OnlineReview Course, Domain 2, Module 2, Lesson 1

The best way to enable the organization to work toward improvement in its security threat and vulnerability management program is to use a capability maturity model to identify a path to an optimized program. A capability maturity model is a framework that helps organizations assess their current level of performance and maturity in a specific domain, and provides guidance and best practices to achieve higher levels of excellence12. A capability maturity model for vulnerability management can help the organization to evaluate its current practices, identify gaps and weaknesses, and implement improvement actions based on the defined criteria and objectives34.
References
1: What is a Capability Maturity Model?1 2: Capability Maturity Model - Wikipedia2 3: Vulnerability Management Maturity Model - SANS Institute4 4: 5 Stages Of Vulnerability Management Maturity Model - SecPod Blog3