make the test test something

tests/run/pyextattrref.pyx

 __doc__ = """
-    >>> 
+    >>> s = Spam(Eggs("ham"))
+    >>> test(s)
+    'ham'
 """
 
 cdef class Eggs:
     cdef object ham
+    def __init__(self, ham):
+        self.ham = ham
 
 cdef class Spam:
     cdef Eggs eggs
+    def __init__(self, eggs):
+        self.eggs = eggs
 
-cdef void tomato(Spam s):
+cdef object tomato(Spam s):
     food = s.eggs.ham
+    return food
+
+def test(Spam s):
+    return tomato(s)