Make infinity dependency optional for range type tests

tests/types/test_int_range.py

@@ -1,12 +1,13 @@
 from pytest import mark
 import sqlalchemy as sa
 intervals = None
+inf = -1
 try:
     import intervals
+    from infinity import inf
 except ImportError:
     pass
 from tests import TestCase
-from infinity import inf
 from sqlalchemy_utils import IntRangeType
 
 

tests/types/test_numeric_range.py

@@ -6,10 +6,10 @@ import sqlalchemy as sa
 intervals = None
 try:
     import intervals
+    from infinity import inf
 except ImportError:
     pass
 from tests import TestCase
-from infinity import inf
 from sqlalchemy_utils import NumericRangeType