Unit testing and SAP software

The ABAP Unit Wiki on the SDN is a good place to start, as well as this ABAP Unit Best Practices article.

SAPTechnical.com also has an ABAP Unit overview.

And finally, you should check out the links in this question.

Just with regards to your reference to Ruby on the SAP ABAP platform, what you are referring to is "Blue Ruby". This is a project of SAP's research labs and you can find information about it on the SAP Developer Network wiki

In my testing a year ago, I found that Blue Ruby was much preferable to ABAPUnit in several ways, including the ability to be more true to test/behavior-driven-development principles by (for example) writing a test for a method before implementing the method.

Ruby, of course, also has far more and more mature TDD/BDD libraries than ABAP, which pretty much just has ABAPUnit and the eCATT tools. These libraries (RSpec, Cucumber, etc) seem to work under Blue Ruby. Both ABAPUnit and Blue Ruby have improved a lot since I looked in to them a year ago, but only for the better, I think.