Clean up session sharing

* Test cases
* Fix premature session.close when caller
  is managing email backend connection
* Ensure session closed correct in exceptions
* Changelog

(Also fixes bug where JSON serialization errors
didn't respect fail_silently.)

djrill/tests/test_mandrill_session_sharing.py

@@ -0,0 +1,72 @@
+from decimal import Decimal
+from mock import patch
+
+from django.core import mail
+
+from .mock_backend import DjrillBackendMockAPITestCase
+
+
+class DjrillSessionSharingTests(DjrillBackendMockAPITestCase):
+    """Test Djrill backend sharing of single Mandrill API connection"""
+
+    @patch('requests.Session.close', autospec=True)
+    def test_connection_sharing(self, mock_close):
+        """Djrill reuses one requests session when sending multiple messages"""
+        datatuple = (
+            ('Subject 1', 'Body 1', 'from@example.com', ['to@example.com']),
+            ('Subject 2', 'Body 2', 'from@example.com', ['to@example.com']),
+        )
+        mail.send_mass_mail(datatuple)
+        self.assertEqual(self.mock_post.call_count, 2)
+        session1 = self.mock_post.call_args_list[0][0]  # arg[0] (self) is session
+        session2 = self.mock_post.call_args_list[1][0]
+        self.assertEqual(session1, session2)
+        self.assertEqual(mock_close.call_count, 1)
+
+    @patch('requests.Session.close', autospec=True)
+    def test_caller_managed_connections(self, mock_close):
+        """Calling code can created long-lived connection that it opens and closes"""
+        connection = mail.get_connection()
+        connection.open()
+        mail.send_mail('Subject 1', 'body', 'from@example.com', ['to@example.com'], connection=connection)
+        session1 = self.mock_post.call_args[0]
+        self.assertEqual(mock_close.call_count, 0)  # shouldn't be closed yet
+
+        mail.send_mail('Subject 2', 'body', 'from@example.com', ['to@example.com'], connection=connection)
+        self.assertEqual(mock_close.call_count, 0)  # still shouldn't be closed
+        session2 = self.mock_post.call_args[0]
+        self.assertEqual(session1, session2)  # should have reused same session
+
+        connection.close()
+        self.assertEqual(mock_close.call_count, 1)
+
+    def test_session_closed_after_exception(self):
+        # fail loud case:
+        msg = mail.EmailMessage('Subject', 'Message', 'from@example.com', ['to1@example.com'],)
+        msg.global_merge_vars = {'PRICE': Decimal('19.99')}  # will cause JSON serialization error
+        with patch('requests.Session.close', autospec=True) as mock_close:
+            with self.assertRaises(TypeError):
+                msg.send()
+        self.assertEqual(mock_close.call_count, 1)
+
+        # fail silently case (EmailMessage caches backend on send, so must create new one):
+        msg = mail.EmailMessage('Subject', 'Message', 'from@example.com', ['to1@example.com'],)
+        msg.global_merge_vars = {'PRICE': Decimal('19.99')}
+        with patch('requests.Session.close', autospec=True) as mock_close:
+            sent = msg.send(fail_silently=True)
+            self.assertEqual(sent, 0)
+        self.assertEqual(mock_close.call_count, 1)
+
+        # caller-supplied connection case:
+        with patch('requests.Session.close', autospec=True) as mock_close:
+            connection = mail.get_connection()
+            connection.open()
+            msg = mail.EmailMessage('Subject', 'Message', 'from@example.com', ['to1@example.com'],
+                                    connection=connection)
+            msg.global_merge_vars = {'PRICE': Decimal('19.99')}
+            with self.assertRaises(TypeError):
+                msg.send()
+            self.assertEqual(mock_close.call_count, 0)  # wait for us to close it
+
+            connection.close()
+            self.assertEqual(mock_close.call_count, 1)