Add a unit test for a multiprocessing bug

Add a test for DM-13316: AST errors when using multiprocessing
to return astshim objects

tests/test_object.py

@@ -1,4 +1,5 @@
 from __future__ import absolute_import, division, print_function
+import multiprocessing
 import unittest
 
 import numpy as np
@@ -152,6 +153,19 @@ def test_ident(self):
         cp = obj.copy()
         self.assertEqual(cp.ident, "initial_ident")
 
+    def test_multiprocessing(self):
+        """Make sure we can return objects from multiprocessing
+
+        This tests DM-13316: AST errors when using multiprocessing
+        to return astshim objects.
+        """
+        numProcesses = 2
+        naxes = 1
+        params = [naxes]*numProcesses
+        pool = multiprocessing.Pool(processes=numProcesses)
+        results = pool.map(ast.UnitMap, params)
+        self.assertEqual(results, [ast.UnitMap(naxes)]*numProcesses)
+
     def test_show(self):
         # pick an object with no floats so we don't have to worry
         # about the float representation