Extend cpp_enums test into a runnable test.

tests/compile/cpp_enums.pyx → tests/run/cpp_enums.pyx

 # tag: cpp
-# mode: compile
+# mode: run
 
 cdef extern from *:
     """
@@ -21,6 +21,14 @@ x = Item1
 y = Item2
 
 
+def compare_enums():
+    """
+    >>> compare_enums()
+    (True, True, True, True)
+    """
+    return x == a, a == Item1, b == y, y == Item2
+
+
 cdef extern from * namespace "Namespace1":
     """
     namespace Namespace1 {
@@ -41,3 +49,10 @@ cdef Enum2 z, w
 z = Item3
 w = Item4
 
+
+def compare_namespace_enums():
+    """
+    >>> compare_namespace_enums()
+    (True, True, True, True)
+    """
+    return z == c, c == Item3, d == w, d == Item4