Ant Build query

Question

excuse my terms with regards to the build tool, as I am new to this.

I have a Java test application, when I use it on eclipse and run the testcases, everything works smooth. This application also can be built with the ANT tool.

Now, the next approach would be to run the cases from the command line. I clean my project, run the ant build. Build shows successful. I navigate to the bin folder and press

java client.Main

It says an error

Error: Unable to initialize the main class client.Main
Caused by: java.lang.NoClassDefFoundError: org/junit/runners/model/InitializationError

I thought it needs some parameters, and passed some arguments. It fails there as well.

PS: I am a fresher, just working on EX colleague's application here with no documentation.

Also, I have the Junit and hamcrest library already added in the build path

Need some guidance