Fix inequality checks for Period and Interval (#688) (#726)

Author: sdispater

pendulum/interval.py

@@ -448,3 +448,6 @@ def __eq__(self, other: object) -> bool:
             )
         else:
             return self.as_duration() == other
+
+    def __ne__(self, other: object) -> bool:
+        return not self.__eq__(other)

tests/interval/test_behavior.py

@@ -52,3 +52,16 @@ def test_equality_to_timedelta():
     period = dt2 - dt1
 
     assert period == timedelta(days=2)
+
+
+def test_inequality():
+    dt1 = pendulum.datetime(2016, 11, 18)
+    dt2 = pendulum.datetime(2016, 11, 20)
+    dt3 = pendulum.datetime(2016, 11, 22)
+
+    period1 = dt2 - dt1
+    period2 = dt3 - dt2
+    period3 = dt3 - dt1
+
+    assert period1 != period2
+    assert period1 != period3