Or if we really want to test these constants, we can use something like this:

if hasattr(resource, 'RLIMIT_NICE'):
    self.assertIsInstance(resource.RLIMIT_NICE, int)

Or if we want to be so strict:

if hasattr(resource, 'RLIMIT_NICE'):
    self.assertTrue(-20 <= resource.RLIMIT_NICE <= 19)

Reference:
http://man7.org/conf/lca2006/Linux_2.6_changes/rlimit_5.html

RLIMIT_NICE (2.6.12)

    Process nice value has range -20 (high) to +19 (low); influences kernel scheduler.