I have both Python 2.7 and 3.3 installed on a Mac.  I'm trying to get Pytest to run my tests under Python 3.3. 
When I run python3 –m py.test it halts, looking for the libs under the 3.3 path.  
When I run pip install –U pytest it installs to the 2.7 path.  
I've seen the write-ups for Virtualenv, but I'm not ready to go there yet.  
Is there another way?
Apart from the genscript option the normal way to go about this is to intall py.test into the python3.3 interpreter's environment.  The problem you have is that the pip you invoke is also a py27 version, so it will install into py27.
So you can start with installing pip into py33 (usually under the alias pip3) and then invoking that pip or you can simply install py and pytest in the py33 environment the old fashioned way: download the packages and run python3.3 setup.py install --user.
You will then still want to make sure you can invoke the correct version of py.test however, either making sure you can call py.test and py.test3 using aliases or so.  Or simply by using pythonX.Y -m pytest.
running pytest with python 3.3