ENH: Use some assertions from ticket 102

tests/test_error_stuff.py

@@ -82,6 +82,8 @@ def test_retrieval_exception_raised():
     # Correct entity causing the error:
     assert not (ee.get_entity() is None)
     assert ee.get_entity().name == propname
+    assert not ee.get_entity().is_valid()
+    assert ee.get_entity().has_errors()
 
 
 def test_insertion_no_exception_raised():