tests: add test for passing user defined classes and instances from parent -> child

It's well known that unpickling data received from an untrusted source is not
secure. But since children trust their parents and ancestors, unpickling data
received from a parent or ancestor should be supported. Add a test for this use
case.

Signed-off-by: Marc Hartmayer <mhartmay@linux.ibm.com>

tests/call_function_test.py

@@ -42,6 +42,14 @@ class TargetClass:
     def add_numbers_with_offset(cls, x, y):
         return cls.offset + x + y
 
+    @classmethod
+    def passing_crazy_type(cls, crazy_cls):
+        return crazy_cls.__name__
+
+    @classmethod
+    def passing_crazy_type_instance(cls, crazy):
+        return crazy.__class__.__name__
+
 
 class CallFunctionTest(testlib.RouterMixin, testlib.TestCase):
 
@@ -58,6 +66,18 @@ class CallFunctionTest(testlib.RouterMixin, testlib.TestCase):
             103,
         )
 
+    def test_succeeds_passing_class(self):
+        self.assertEqual(
+            self.local.call(TargetClass.passing_crazy_type, CrazyType),
+            'CrazyType'
+        )
+
+    def test_succeeds_passing_class_instance(self):
+        self.assertEqual(
+            self.local.call(TargetClass.passing_crazy_type_instance, CrazyType()),
+            'CrazyType'
+        )
+
     def test_crashes(self):
         exc = self.assertRaises(mitogen.core.CallError,
             lambda: self.local.call(function_that_fails))