Test if code is executed from within a py.test session

I'd like to connect to a different database if my code is running under py.test. Is there a function to call or an environment variable that I can test that will tell me if I'm running under a py.test session? What's the best way to handle this?

A solution came from RTFM, although not in an obvious place. The manual also had an error in code, corrected below.

Detect if running from within a pytest run

Usually it is a bad idea to make application code behave differently if called from a test. But if you absolutely must find out if your application code is running from a test you can do something like this:

# content of conftest.py
def pytest_configure(config):
    import sys
    sys._called_from_test = True

def pytest_unconfigure(config):
    import sys  # This was missing from the manual
    del sys._called_from_test

and then check for the sys._called_from_test flag:

if hasattr(sys, '_called_from_test'):
    # called from within a test run
else:
    # called "normally"

accordingly in your application. It’s also a good idea to use your own application module rather than sys for handling flag.