Also document the not-a-method case.

docs/verify.rst

@@ -151,6 +151,14 @@ different type of exception, so we need an updated helper.
    ...    except BrokenMethodImplementation as e:
    ...        print(e)
 
+Not being callable is an error.
+
+.. doctest::
+
+   >>> Foo.simple = 42
+   >>> verify_foo()
+   The object <Foo...> violates its contract in IFoo.simple(arg1): implementation is not a method.
+
 Taking too few arguments is an error.
 
 .. doctest::

src/zope/interface/verify.py

@@ -110,7 +110,7 @@ def _verify(iface, candidate, tentative=False, vtype=None):
             continue
         else:
             if not callable(attr):
-                raise BrokenMethodImplementation(name, "Not a method", candidate)
+                raise BrokenMethodImplementation(desc, "implementation is not a method", candidate)
             # sigh, it's callable, but we don't know how to introspect it, so
             # we have to give it a pass.
             continue