Add pre_send and post_send signals

Closes #8

tests/test_send_signals.py

@@ -0,0 +1,112 @@
+from django.dispatch import receiver
+
+from anymail.backends.test import TestBackend
+from anymail.exceptions import AnymailCancelSend, AnymailRecipientsRefused
+from anymail.message import AnymailRecipientStatus
+from anymail.signals import pre_send, post_send
+
+from .test_general_backend import TestBackendTestCase
+
+
+class TestPreSendSignal(TestBackendTestCase):
+    """Test Anymail's pre_send signal"""
+
+    def test_pre_send(self):
+        """Pre-send receivers invoked for each message, before sending"""
+        @receiver(pre_send, weak=False)
+        def handle_pre_send(sender, message, esp_name, **kwargs):
+            self.assertEqual(self.get_send_count(), 0)  # not sent yet
+            self.assertEqual(sender, TestBackend)
+            self.assertEqual(message, self.message)
+            self.assertEqual(esp_name, "Test")  # the TestBackend's ESP is named "Test"
+            self.receiver_called = True
+        self.addCleanup(pre_send.disconnect, receiver=handle_pre_send)
+
+        self.receiver_called = False
+        self.message.send()
+        self.assertTrue(self.receiver_called)
+        self.assertEqual(self.get_send_count(), 1)  # sent now
+
+    def test_modify_message_in_pre_send(self):
+        """Pre-send receivers can modify message"""
+        @receiver(pre_send, weak=False)
+        def handle_pre_send(sender, message, esp_name, **kwargs):
+            message.to = [email for email in message.to if not email.startswith('bad')]
+            message.body += "\nIf you have received this message in error, ignore it"
+        self.addCleanup(pre_send.disconnect, receiver=handle_pre_send)
+
+        self.message.to = ['legit@example.com', 'bad@example.com']
+        self.message.send()
+        params = self.get_send_params()
+        self.assertEqual([email.email for email in params['to']],  # params['to'] is ParsedEmail list
+                         ['legit@example.com'])
+        self.assertRegex(params['text_body'],
+                         r"If you have received this message in error, ignore it$")
+
+    def test_cancel_in_pre_send(self):
+        """Pre-send receiver can cancel the send"""
+        @receiver(pre_send, weak=False)
+        def cancel_pre_send(sender, message, esp_name, **kwargs):
+            raise AnymailCancelSend("whoa there")
+        self.addCleanup(pre_send.disconnect, receiver=cancel_pre_send)
+
+        self.message.send()
+        self.assertEqual(self.get_send_count(), 0)  # send API not called
+
+
+class TestPostSendSignal(TestBackendTestCase):
+    """Test Anymail's post_send signal"""
+
+    def test_post_send(self):
+        """Post-send receiver called for each message, after sending"""
+        @receiver(post_send, weak=False)
+        def handle_post_send(sender, message, status, esp_name, **kwargs):
+            self.assertEqual(self.get_send_count(), 1)  # already sent
+            self.assertEqual(sender, TestBackend)
+            self.assertEqual(message, self.message)
+            self.assertEqual(status.status, {'sent'})
+            self.assertEqual(status.message_id, 1)  # TestBackend default message_id
+            self.assertEqual(status.recipients['to@example.com'].status, 'sent')
+            self.assertEqual(status.recipients['to@example.com'].message_id, 1)
+            self.assertEqual(esp_name, "Test")  # the TestBackend's ESP is named "Test"
+            self.receiver_called = True
+        self.addCleanup(post_send.disconnect, receiver=handle_post_send)
+
+        self.receiver_called = False
+        self.message.send()
+        self.assertTrue(self.receiver_called)
+
+    def test_post_send_exception(self):
+        """All post-send receivers called, even if one throws"""
+        @receiver(post_send, weak=False)
+        def handler_1(sender, message, status, esp_name, **kwargs):
+            raise ValueError("oops")
+        self.addCleanup(post_send.disconnect, receiver=handler_1)
+
+        @receiver(post_send, weak=False)
+        def handler_2(sender, message, status, esp_name, **kwargs):
+            self.handler_2_called = True
+        self.addCleanup(post_send.disconnect, receiver=handler_2)
+
+        self.handler_2_called = False
+        with self.assertRaises(ValueError):
+            self.message.send()
+        self.assertTrue(self.handler_2_called)
+
+    def test_rejected_recipients(self):
+        """Post-send receiver even if AnymailRecipientsRefused is raised"""
+        @receiver(post_send, weak=False)
+        def handle_post_send(sender, message, status, esp_name, **kwargs):
+            self.receiver_called = True
+        self.addCleanup(post_send.disconnect, receiver=handle_post_send)
+
+        self.message.test_response = {
+            'recipient_status': {
+                'to@example.com': AnymailRecipientStatus(message_id=None, status='rejected')
+            }
+        }
+
+        self.receiver_called = False
+        with self.assertRaises(AnymailRecipientsRefused):
+            self.message.send()
+        self.assertTrue(self.receiver_called)