PBR is a library that injects some useful and sensible default behaviors into your setuptools run. It started off life as the chunks of code that were copied between all of the OpenStack projects. Around the time that OpenStack hit 18 different projects each with at least 3 active branches, it seems like a good time to make that code into a proper re-usable library.
PBR is only mildly configurable. The basic idea is that there's a decent way to run things and if you do, you should reap the rewards, because then it's simple and repeatable. If you want to do things differently, cool! But you've already got the power of python at your fingertips, so you don't really need PBR.
PBR builds on top of the work that d2to1 started to provide for declarative configuration. d2to1 is itself an implementation of the ideas behind distutils2. Although distutils2 is now abandoned in favor of work towards PEP 426 and Metadata 2.0, declarative config is still a great idea and specifically important in trying to distribute setup code as a library when that library itself will alter how the setup is processed. As Metadata 2.0 and other modern Python packaging PEPs come out, pbr aims to support them as quickly as possible.
You can read more in the documentation.
The testing system is based on a combination of tox and testr. The canonical approach to running tests is to simply run the command tox. This will create virtual environments, populate them with depenedencies and run all of the tests that OpenStack CI systems run. Behind the scenes, tox is running testr run --parallel, but is set up such that you can supply any additional testr arguments that are needed to tox. For example, you can run: tox -- --analyze-isolation to cause tox to tell testr to add --analyze-isolation to its argument list.
It is also possible to run the tests inside of a virtual environment you have created, or it is possible that you have all of the dependencies installed locally already. If you'd like to go this route, the requirements are listed in requirements.txt and the requirements for testing are in test-requirements.txt. Installing them via pip, for instance, is simply:
pip install -r requirements.txt -r test-requirements.txt
In you go this route, you can interact with the testr command directly. Running testr run will run the entire test suite. testr run --parallel will run it in parallel (this is the default incantation tox uses.) More information about testr can be found at: http://wiki.openstack.org/testr