#!/usr/bin/env python

"""
<Program Name>
  aggregate_tests.py

<Author>
  Konstantin Andrianov.
  Zane Fisher.

<Started>
  January 26, 2013.

  August 2013.
  Modified previous behavior that explicitly imported individual
  unit tests. -Zane Fisher

<Copyright>
  See LICENSE for licensing information.

<Purpose>
  Run all the unit tests from every .py file beginning with "test_" in
  'securesystemslib/tests'.
"""

# Help with Python 3 compatibility, where the print statement is a function, an
# implicit relative import is invalid, and the '/' operator performs true
# division.  Example:  print 'hello world' raises a 'SyntaxError' exception.
from __future__ import print_function
from __future__ import absolute_import
from __future__ import division
from __future__ import unicode_literals

import sys
import unittest

if __name__ == '__main__':
  suite = unittest.TestLoader().discover("tests", top_level_dir=".")
  all_tests_passed = unittest.TextTestRunner(verbosity=1).run(suite).wasSuccessful()
  if not all_tests_passed:
    sys.exit(1)

#!/usr/bin/env python

"""
<Program Name>
  aggregate_tests.py

<Author>
  Konstantin Andrianov.
  Zane Fisher.

<Started>
  January 26, 2013.

  August 2013.
  Modified previous behavior that explicitly imported individual
  unit tests. -Zane Fisher

<Copyright>
  See LICENSE for licensing information.

<Purpose>
  Run all the unit tests from every .py file beginning with "test_" in
  'securesystemslib/tests'.
"""

# Help with Python 3 compatibility, where the print statement is a function, an
# implicit relative import is invalid, and the '/' operator performs true
# division.  Example:  print 'hello world' raises a 'SyntaxError' exception.
from __future__ import print_function
from __future__ import absolute_import
from __future__ import division
from __future__ import unicode_literals

import os
import sys
import unittest
import subprocess

def check_usable_gpg():
  """Set `TEST_SKIP_GPG` environment variable if neither gpg2 nor gpg is
  available. """
  os.environ["TEST_SKIP_GPG"] = "1"
  for gpg in ["gpg2", "gpg"]:
    try:
      subprocess.check_call([gpg, "--version"])

    except OSError:
      pass

    else:
      # If one of the two exists, we can unset the skip envvar and ...
      os.environ.pop("TEST_SKIP_GPG", None)
      # ... abort the availability check.:
      break

if __name__ == '__main__':
  check_usable_gpg()
  suite = unittest.TestLoader().discover("tests", top_level_dir=".")
  all_tests_passed = unittest.TextTestRunner(verbosity=1).run(suite).wasSuccessful()
  if not all_tests_passed:
    sys.exit(1)

Copy and call in-toto's check_usable_gpg function