Add test for infinite looping on attribute access

IPython/core/tests/test_oinspect.py

@@ -186,6 +186,23 b' class NoBoolCall:'
         raise NotImplementedError('Must be implemented')
 
 
+class SerialLiar(object):
+    """Attribute accesses always get another copy of the same class.
+
+    unittest.mock.call does something similar, but it's not ideal for testing
+    as the failure mode is to eat all your RAM. This gives up after 10k levels.
+    """
+    def __init__(self, max_fibbing_twig, lies_told=0):
+        if lies_told > 10000:
+            raise RuntimeError('Nose too long, honesty is the best policy')
+        self.max_fibbing_twig = max_fibbing_twig
+        self.lies_told = lies_told
+        max_fibbing_twig[0] = max(max_fibbing_twig[0], lies_told)
+
+    def __getattr__(self, item):
+        return SerialLiar(self.max_fibbing_twig, self.lies_told + 1)
+
+
 def check_calltip(obj, name, call, docstring):
     """Generic check pattern all calltip tests will use"""
     info = inspector.info(obj, name)
@@ -297,6 +314,14 b' def test_info_awkward():'
 def test_bool_raise():
     inspector.info(NoBoolCall())
 
+def test_info_serialliar():
+    fib_tracker = [0]
+    i = inspector.info(SerialLiar(fib_tracker))
+
+    # Nested attribute access should be cut off at 100 levels deep to avoid
+    # infinite loops: https://github.com/ipython/ipython/issues/9122
+    nt.assert_less(fib_tracker[0], 9000)
+
 def test_calldef_none():
     # We should ignore __call__ for all of these.
     for obj in [f, SimpleClass().method, any, str.upper]: