[bugfix] Checking MarkDecorator equality returns False for non-MarkDecorator object

_pytest/mark.py

@@ -330,7 +330,7 @@ class MarkDecorator:
         return self.name  # for backward-compat (2.4.1 had this attr)
 
     def __eq__(self, other):
-        return self.mark == other.mark
+        return self.mark == other.mark if isinstance(other, MarkDecorator) else False
 
     def __repr__(self):
         return "<MarkDecorator %r>" % (self.mark,)

changelog/2758.bugfix

@@ -0,0 +1 @@
+The equality checking function (``__eq__``) of ``MarkDecorator`` returns ``False`` if one object is not an instance of ``MarkDecorator``.

testing/test_mark.py

@@ -812,3 +812,15 @@ def test_legacy_transfer():
     assert fake_method.fun
     # pristine marks dont transfer
     assert fake_method.pytestmark == [pytest.mark.fun.mark]
+
+
+class TestMarkDecorator(object):
+
+    @pytest.mark.parametrize('lhs, rhs, expected', [
+        (pytest.mark.foo(), pytest.mark.foo(), True),
+        (pytest.mark.foo(), pytest.mark.bar(), False),
+        (pytest.mark.foo(), 'bar', False),
+        ('foo', pytest.mark.bar(), False)
+    ])
+    def test__eq__(self, lhs, rhs, expected):
+        assert (lhs == rhs) == expected