119: Added ProxyTarget.implemented_by() classmethod; added corresponding unit tests

ipalib/plugable.py

@@ -135,6 +135,18 @@ class ProxyTarget(ReadOnly):
             "must be str, frozenset, or have frozenset '__public__' attribute"
         )
 
+    @classmethod
+    def implemented_by(cls, arg):
+        if inspect.isclass(arg):
+            subclass = arg
+        else:
+            subclass = arg.__class__
+        assert issubclass(subclass, cls), 'must be subclass of %r' % cls
+        for name in cls.__public__:
+            if not hasattr(subclass, name):
+                return False
+        return True
+
 
 class Proxy(ReadOnly):
     """

ipalib/tests/test_plugable.py

@@ -183,6 +183,49 @@ class test_ProxyTarget(ClassChecker):
             assert ex.implements(any_object)
             assert ex.implements(any_object())
 
+    def test_implemented_by(self):
+        """
+        Tests the `implemented_by` classmethod.
+        """
+        class base(self.cls):
+            __public__ = frozenset((
+                'attr0',
+                'attr1',
+                'attr2',
+            ))
+
+        class okay(base):
+            def attr0(self):
+                pass
+            def __get_attr1(self):
+                assert False # Make sure property isn't accesed on instance
+            attr1 = property(__get_attr1)
+            attr2 = 'hello world'
+            another_attr = 'whatever'
+
+        class fail(base):
+            def __init__(self):
+                # Check that class, not instance is inspected:
+                self.attr2 = 'hello world'
+            def attr0(self):
+                pass
+            def __get_attr1(self):
+                assert False # Make sure property isn't accesed on instance
+            attr1 = property(__get_attr1)
+            another_attr = 'whatever'
+
+        # Test that AssertionError is raised trying to pass something not
+        # subclass nor instance of base:
+        raises(AssertionError, base.implemented_by, object)
+
+        # Test on subclass with needed attributes:
+        assert base.implemented_by(okay) is True
+        assert base.implemented_by(okay()) is True
+
+        # Test on subclass *without* needed attributes:
+        assert base.implemented_by(fail) is False
+        assert base.implemented_by(fail()) is False
+
 
 class test_Proxy(ClassChecker):
     """