Python unittest slow and tests failing when running under TeamCity

Question

I have a testsuite written in Python/unittest+TeamcityTestRunner and running under Linux.

Most of the tests involve running a separate thread subprocess.Popen with the tested app (which is a console app, itself running multiple subprocesses/plugins - C++ code) and checking if: a subprocess/plugin of the app is restarted when killed, creating the files it has to create, etc.

The problem is that when I run the test suite normally - ssh to the build machine (VM), running the script against the binary/app - all tests pass.

When I run the same test suite against the same binary/app from TeamCity, all tests fail.

After some debugging, I found out that the app runs/loads very slowly when run from TeamCity-unittest-subprocess.Popen.

What can be the culprit of this? Has the TeamcityTestRunner that much additional overhead to cause this behavior? What can I do about it?

Answer 1

The culprit seems to be the overhead caused by running under TeamCity, on a slow VM and the overhead of subprocess.Popen

the old code which did not work for me was:

cmd = [binary, 'param1']
outfile = open(redirect_to, 'w')
subprocess.call(cmd, stdout=outfile)

the new, much faster in practice as it turned out is:

cmd = [binary, 'param1']
redirect_to = '/tmp/out'
p = os.popen(' '.join(cmd) + '2>&1 >' + redirect_to)
p.close()

more info here: http://essays.ajs.com/2011/02/python-subprocess-vs-ospopen-overhead.html