source code with its unit test

There are quite a few open source Java Numerics libraries out there.
 
You might consider this one which has some tests attached to it. Apache Commons Math
 
If the style of tests is not to your this page could be useful.http://math.nist.gov/javanumerics/
 
The key idea is that open source Java Math libraries usually come with some sort of test routine. Sometimes the testing isformal as in unit tests and sometimes informal.
 
Hope this helps.
 
Ken