testing: Only check for ValueError when strict

stratis only checks pool features strictly when
STRATIS_STRICT_POOL_FEATURES is set, so that behavior should be tested
only under these conditions.

Signed-off-by: mulhern <amulhern@redhat.com>

Author: mulkieran

tests/whitebox/unittest/test_constants.py

@@ -16,6 +16,7 @@
 """
 
 # isort: STDLIB
+import os
 import unittest
 
 # isort: LOCAL
@@ -97,8 +98,9 @@ def test_str_method(self):
         for feature in PoolFeature:
             if feature is PoolFeature.UNRECOGNIZED:
                 self.assertIsInstance(str(feature), str)
-                with self.assertRaises(ValueError):
-                    PoolFeature("unknown")
+                if bool(int(os.environ.get("STRATIS_STRICT_POOL_FEATURES", False))):
+                    with self.assertRaises(ValueError):
+                        PoolFeature("unknown")
             else:
                 self.assertEqual(str(feature), feature.value)
                 self.assertEqual(PoolFeature(feature.value), feature)