In Python, add extra tests to a unittest.main() test run (without depending on global state).

runtests.py

import unittest


def run_tests(data):
    extra_tests = create_extra_tests(data)
    test_program_class = make_test_program_class(extra_tests)

    # In this constructor call you can include any of the arguments supported
    # by unittest.main().
    test_program_class()  # runs tests.


def make_test_program_class(extra_tests):
    """
    Return a unittest.TestProgram subclass that adds a list of custom tests.

    Arguments:

      extra_tests: an iterable of TestCase and TestSuite instances to add in
        addition to the usual tests loaded when calling createTests().
        cf. http://docs.python.org/py3k/library/unittest.html#unittest.TestSuite.addTests

    """
    class MyTestProgram(unittest.TestProgram):

        def createTests(self):
            super(MyTestProgram, self).createTests()
            self.test.addTests(extra_tests)

    return MyTestProgram