TST: check consistency of (Atom, Structure) pickle

This fails in Python 3.7.

Author: pavoljuhas

src/diffpy/structure/tests/teststructure.py

@@ -18,6 +18,7 @@
 
 
 import copy
+import pickle
 import unittest
 import numpy
 
@@ -656,6 +657,17 @@ def test_Bij(self):
         self.assertFalse(numpy.any(stru.U != 0.0))
         return
 
+
+    def test_pickling(self):
+        """Make sure Atom in Structure can be consistently pickled.
+        """
+        stru = self.stru
+        a = stru[0]
+        self.assertTrue(a is stru[0])
+        a1, stru1 = pickle.loads(pickle.dumps((a, stru)))
+        self.assertTrue(a1 is stru1[0])
+        return
+
 # End of class TestStructure
 
 # ----------------------------------------------------------------------------