tests/silenttestrunner.py

sparse: use None as the sparse matcher value when disabled

This create a clear signal for when the feature is unused. We could also create
an `alwaysmatcher`, but using None is more explicit, so I went for it.

import os
import sys
import unittest


def main(modulename):
    '''run the tests found in module, printing nothing when all tests pass'''
    module = sys.modules[modulename]
    suite = unittest.defaultTestLoader.loadTestsFromModule(module)
    results = unittest.TestResult()
    suite.run(results)
    if results.errors or results.failures:
        for tc, exc in results.errors:
            print('ERROR:', tc)
            print()
            sys.stdout.write(exc)
        for tc, exc in results.failures:
            print('FAIL:', tc)
            print()
            sys.stdout.write(exc)
        sys.exit(1)


if os.environ.get('SILENT_BE_NOISY'):
    main = unittest.main