I am looking for some tutorials and guides for unit testing on SAP platform. So far, I have found some mention of ABAP Unit and of Ruby programming language being implemented on SAP software, making it much more interesting option for unit testing SAP software. However, the information is quite scarce and I would appreciate some help on the subject.
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.