Regression testing is the most appropriate testing method for assessing whether system integrity has been maintained after changes have been made. Regression testing is a type of software testing that ensures that previously developed and tested software still performs as expected after a change1 Regression testing helps to detectany defects or errors that may have been introduced or uncovered due to the change2 Regression testing can be performed at different levels of testing, such as unit, integration, system, and acceptance3 Unit testing is a type of software testing that verifies the functionality of individual components or units of code. Unit testing is usually performed by developers before integrating the code with other components. Unit testing helps to identify and fix errors at an early stage of development, but it does not ensure that the system as a whole works as expected after a change.
Integration testing is a type of software testing that verifies the functionality, performance, and reliability of the interactions between different components or units of code. Integration testing is usually performed after unit testing and before system testing. Integration testing helps to identify and fix errors that may occur when different components are integrated, but it does not ensure that the system as a whole works as expected after a change.
Acceptance testing is a type of software testing that verifies whether the system meets the user requirements and expectations. Acceptance testing is usually performed by end-users or customersafter system testing and before deploying the system to production. Acceptance testing helps to ensure that the system delivers the desired value and quality to the users, but it does not ensure that the system as a whole works as expected after a change.
References: 1: What is Regression Testing? Test Cases (Example) - Guru99 2: What is Regression Testing? Definition, Tools, Examples - Katalon 3: Regression testing - Wikipedia : What is Unit Testing?
Definition, Types, Tools and Examples - Guru99 : What is Integration Testing? Definition, Types, Tools and Examples - Guru99 : What is Acceptance Testing? Definition, Types, Tools and Examples - Guru99

The best approach for management in developing a test plan is to use processing parameters that are simulated by production entities and customers. This is because using realistic data and scenarios can help to evaluate the functionality, performance, reliability, and security of the new system under actual operating conditions and expectations. Using processing parameters that are randomly selected by a test generator, provided by the vendor of the application, or randomly selected by the user may not be sufficient or representative of the production environment and may not reveal all the potential issues or defects of the new system. References: [ISACA CISA Review Manual 27th Edition], page 266.

Control self-assessment (CSA) is a technique that enables business managers and staff to assess and improve the effectiveness of their own controls and risk management processes. CSA can best enable the timely identification of risk exposure, as it allows for continuous monitoring and reporting of risks by those who are closest to the business processes and activities. External audit review, internal audit review, and stress testing are also useful methods for identifying risk exposure, but they are not as timely as CSA, as they are performed periodically or on demand by external or internal parties who may not have as much insight into the business operations and environment. References: ISACA CISA Review Manual 27th Edition, page 95.

The authority given to the audit function is one of the components that is found in an audit charter. According to the IIA, the audit charter is a formal document that defines internal audit's purpose, authority, responsibility and position within the organization1. The authority given to the audit function includes the scope of its activities, the access to records, personnel and physical properties relevant to its work, and the independence and objectivity of its staff2. The authority given to the audit function helps to ensure that internal auditors can perform their duties effectively and efficiently, and that they can provide assurance and consulting services that add value and improve the organization's operations3.
The other options are not found in an audit charter. The process of developing the annual audit plan is not part of the audit charter, but rather a separate document that outlines the methodology, criteria and resources for selecting and prioritizing audit engagements based on a risk assessment4. Required training for audit staff is not part of the audit charter, but rather a component of the quality assurance and improvement program that evaluates the competence and performance of internal auditors and provides them with opportunities for professional development5. Audit objectives and scope are not part of the audit charter, but rather specific elements of each individual audit engagement that define the expected outcomes and the boundaries of the audit work.

Integration testing is the best way to ensure that an application is performing according to its specifications, because it tests the interaction and compatibility of different modules or components of the application. Unit testing, pilot testing and system testing are also important, but they do not cover the whole functionality and integration of the application as well as integration testing does. References: CISA Review Manual (Digital Version)1, Chapter 4, Section 4.2.3