Add test case for combined plus minus prefix

Author: cknv

tests/validators/test_int.py

@@ -48,6 +48,7 @@
         ('+4_2.0', 42),
         ('+04_2.0', 42),
         ('++4_2', Err('Input should be a valid integer, unable to parse string as an integer')),
+        ('+-1', Err('Input should be a valid integer, unable to parse string as an integer')),
         ('4_2', 42),
         ('0_42', 42),
         ('4_2.0', 42),