Python testing application: Can't find a downloaded test file.

This code works fine outside of Teamcity agent:

def create_new_csv_file(self, dir='/tmp', file_name='test.csv'):
  os.chdir(dir)
  new_file = file_name
  if os.path.exists(new_file):
    os.remove(new_file)
  open(new_file, 'w').close()

Apparently, instead of being sent to os /tmp directory it goes to /private/tmp 
which isn't visible to the test script so the upload fails.

Any suggestions?