Numbering conventions for automated testing?

I've read a lot about automated testing and have some automated tests on custom work already.
However, I've noticed the standard test codeunits are in the 130.000/140.000 range. According to this >> https://msdn.microsoft.com/en-us/library/ee414238(v=nav.90).aspx << document, this is Microsoft Certified Partner Design area.

Are there any numbering conventions for test codeunits? If so, what are they? Or should I keep test codeunits for our add-on in our add-on range?