def test__extract(self): system_commands = [] def fake_system(cmd): system_commands.append(cmd) original_system = os.system os.system = fake_system filenames = ['archive.rar', 'archive.r00', 'archive.r01', 'archive.r02',] archive = RarArchive('archive', './path', filenames) self.assertTrue(archive._extract()) self.assertEquals(system_commands, ['unrar e ./path/archive.rar']) os.system = original_system