The IS auditor should inform audit management of the earlier involvement in designing the application. This is to ensure that there is no conflict of interest or bias that may affect the objectivity or independence of the audit.
Audit management can then decide whether to assign a different auditor or to proceed with the same auditor with appropriate safeguards. The other options are not appropriate for the IS auditor to do in this situation.
Refusing the assignment to avoid conflict of interest is an extreme measure that may not be necessary or feasible, especially if there are no other qualified auditors available. Using the knowledge of the application to carry out the audit is risky, as it may lead to overlooking or ignoring potential issues or errors in the application. Modifying the scope of the audit is not advisable, as it may compromise the quality or completeness of the audit. References: CISA Review Manual (Digital Version), Chapter 2, Section 2.1

Explanation
The most conclusive audit procedure for evaluating the effectiveness of an e-commerce application system's edit routine is to use test transactions. A test transaction is a simulated input that is processed by the system to verify its output and performance1. By using test transactions, an auditor can directly observe how the edit routine checks the validity, accuracy, and completeness of data entered by users, and how it handles incorrect or invalid data. A test transaction can also help measure the efficiency, reliability, and security of the edit routine, as well as identify any errors or weaknesses in the system.
The other options are not as conclusive as using test transactions, as they rely on indirect or secondary sources of information. Reviewing program documentation is an audit procedure that involves examining the written description of the system's design, specifications, and functionality2. However, program documentation may not reflect the actual implementation or operation of the system, and it may not reveal any discrepancies or defects in the edit routine. Interviews with knowledgeable users is an audit procedure that involves asking questions to the people who use or manage the system3. However, interviews with knowledgeable users may not provide sufficient or objective evidence of the edit routine's effectiveness, and they may be influenced by personal opinions or biases. Reviewing source code is an audit procedure that involves analyzing the programming language and logic of the system4. However, reviewing source code may not be feasible or practical for complex or large systems, and it may not demonstrate how the edit routine performs in real scenarios.

Section: Protection of Information Assets
Explanation:
Federal Information Processing Standards (FIPS) are publicly announced standards developed by the
United States Federal government for use by all nonmilitary government agencies and by government
contractors. Many FIPS standards are modified versions of standards used in the wider community.

Section: Information System Acquisition, Development and Implementation