public function test_has_group()
{
	Cache::expire('*', 'foo', 'glob');
	$this->assertFalse(Cache::has_group('foo'), 'The cache has a group that was explicitly expired.');
	Cache::set(array('foo', 'bar'), 'a value');
	$this->assertTrue(Cache::has_group('foo'), 'The cache does not have a group that was explicitly set.');
}