Missing target class to test in my test application

Hi all,
I have a project (that compiles and runs in the emulator.)
I have a test project that tests part of this project. This test project also compiles with no problems, but when I try to run (test) it in the emulator, I get a NoClassDefFoundError exception on one of the classes my test class tests (I hope that made sense!) when it starts to run in the emulator. This is coming out of the adb log.
I looked in the bin directory (of the test project) for the missing class, but could not find it... Should it be there?
I found no reference (apk, etc) of the project I am trying to test either in the test projects bin directory.
How does the test project get the classes it needs to test against (in the classpath, I assume.) How do the tested classes get moved to the emulator?
I did try running the app before testing, so I know it is installed and runs correctly.
BTW, I am using netbeans with the nbandroid plugin.

thanks for any suggestions or help you may have.
Jordan