Testing for Active Directory Schema Extension Conflicts
http://technet.microsoft.com/en-us/library/testing-for-active-directory-schema-extension-conflicts(WS.10).aspx

This topic explains how you can test a potential Active Directory® schema extension for schema conflicts before you apply the extension to your production schema. There are two options for testing a schema extension before you apply it. Depending on how the application exposes information about the schema extension, you might use one option or you might use both options to perform more comprehensive testing.

1. If the application schema extension is provided in .ldf files that you can read directly, then you can run the Windows PowerShell™ script that is included in this topic to analyze the schema extension and report about any conflicts. Many Microsoft® applications, such as Microsoft Exchange Server and Microsoft Office Communications Server, provide the .ldf files that you can analyze before you apply the required schema extension. As a best practice, use this option for Microsoft products that provide the .ldf files.
   
2. If the application schema extension is not provided in the .ldf files, then you can create a test lab that mirrors the Active Directory schema in your production environment and test the application in the test lab. Generally, a test lab that mirrors your production environment is recommended for all software testing. This helps you to perform more comprehensive application testing, such as testing an application for networking or policy conflicts. But comprehensive application testing is not within the scope of this topic. This topic explains only the steps necessary to create the Active Directory schema for the test lab.