Ensure outerHTML in base Node class (with test).

Author: ntoll

polyplug.py

@@ -294,6 +294,10 @@ def __init__(self, **kwargs):
         self._node = kwargs
         self.parent = kwargs.get("parent")
 
+    @property
+    def outerHTML(self):
+        return NotImplemented
+
     @property
     def as_dict(self):
         return NotImplemented

tests/test_polyplug.py

@@ -202,6 +202,7 @@ def test_node():
     assert n._node["a"] == 1
     assert n._node["b"] == 2
     assert n.parent is None
+    assert n.outerHTML is NotImplemented
     assert n.as_dict is NotImplemented