Final answer:
Security testing, including penetration testing and fuzz testing, is the most effective method for Logan to assess his web application's input and data validation.
Step-by-step explanation:
For Logan to test and evaluate his company's web application, particularly for input and data validation, the most effective method would be to conduct security testing specifically focused on areas such as penetration testing, vulnerability scanning, or using automated tools that simulate attacks on the application. This type of testing is designed to uncover security weaknesses and ensure that the application is robust against various forms of attack.
It is also pertinent to examine the application's response to unexpected or malformed input, which can be done through fuzz testing where random, invalid, or unexpected data is inputted to the system to verify that the application handles it gracefully without exposing security holes or causing crashes.