You can validate a user-defined function from the following areas:
Expression Editor when you create or edit a user-defined function
Tools menu
Query Results window
View History window
When you validate a user-defined function, the PowerCenter Client does not validate other user-defined functions and expressions that use the function. If a user-defined function is invalid, any user-defined function and expression that uses the function is also invalid. Similarly, mappings and workflows that use the user-defined function are invalid.