How to use the discover.defaultTestLoader function in discover

# Without any tests listed as arguments, do discovery
    if len(testargs) == 0:
        if scenario != '':
            sys.stderr.write(
                'run.py: specifying a scenario requires a test name\n')
            usage()
            sys.exit(2)
        from discover import defaultTestLoader as loader
        suites = loader.discover(suitedir)
        suites = sorted(suites, key=lambda c: str(list(c)[0]))
        if configfile != None:
            suites = configApply(suites, configfile, configwrite)
        tests.addTests(restrictScenario(generate_scenarios(suites), ''))
    else:
        for arg in testargs:
            testsFromArg(tests, loader, arg, scenario)

    # Shuffle the tests and create a new suite containing every Nth test from
    # the original suite
    if random_sample > 0:
        random_sample_tests = []
        for test in tests:
            random_sample_tests.append(test)
        random.shuffle(random_sample_tests)
        tests = unittest.TestSuite(random_sample_tests[::random_sample])
    if debug:
        import pdb
        pdb.set_trace()
    if dryRun:
        # We have to de-dupe here as some scenarios overlap in the same suite
        dryOutput = set()
        for test in tests: