# Extending Rational® Integration Tester functionality by using custom functions

You can add more calculations and operations to tests by using the Rational®
Integration Tester custom function class. Rational®
Integration Tester custom function is a Java™ class that extends the `com.ghc.ghTester.expressions`

function.

Note: All custom functions can be called from any of the supported scripting languages in Rational®
Integration Tester.

The following steps provide an overview of how to develop a function for use in Rational® Integration Tester:

- Create a plug-in, which is a Java™ code wrapper that allows the plug-in to be loaded into Rational® Integration Tester. Using the Eclipse IDE for Java™ EE is the easiest way to create a plug-in, but you can also create a plug-in from a different IDE.
- Develop your function class, which involves creating a Java™ class and implementing the function behavior. If you have an existing function and want to modify it to work with Rational® Integration Tester, you must convert existing function classes with Eclipse.
- Create a function extension to provide Rational® Integration Tester with details about your function, such as its name and the class that implements the function.
- Configure and use the function in Rational® Integration Tester, which lets Rational® Integration Tester load your function to be used inside your Rational® Integration Tester project.