[chirp_devel] run_tests: No module named serial

[chirp.cordless at xoxy.net]

I just did a clean clone of the repository.

Per the process outlined at
http://chirp.danplanet.com/projects/chirp/wiki/DevelopersProcess
I thought I'd see how the tests run before I make any changes:

dan[tests]$  run_tests
Traceback (most recent call last):
  File "./run_tests", line 20, in <module>
    from serial import Serial
ImportError: No module named serial

I searched the developer mail archive, and looked at the
hg history info for the file, I don't see anything related.
I'm probably missing something silly, but I don't know what it is.

I'm on a Mac running OS X 10.9.2
Chirp runs ok, it says I'm using (Python 2.7.2).

What am I missing?

-dan