Clean up and document Anymail's test EmailBackend

* Change Anymail's test EmailBackend to collect sent messages in
  django.core.mail.outbox, same as Django's own locmem EmailBackend.
  (So Django's test runner will automatically clear accumulated mail
  between test cases.)

* Rename EmailMessage `test_response` attr to `anymail_test_response`
  to avoid conflicts, and record merged ESP send params in
  new `anymail_send_params` attr.

* Add docs

Closes #36.

anymail/backends/test.py

@@ -1,37 +1,42 @@
-from anymail.exceptions import AnymailAPIError
-from anymail.message import AnymailRecipientStatus
+from django.core import mail
 
 from .base import AnymailBaseBackend, BasePayload
+from ..exceptions import AnymailAPIError
+from ..message import AnymailRecipientStatus
 from ..utils import get_anymail_setting
 
 
 class EmailBackend(AnymailBaseBackend):
     """
-    Anymail backend that doesn't do anything.
+    Anymail backend that simulates sending messages, useful for testing.
 
-    Used for testing Anymail common backend functionality.
+    Sent messages are collected in django.core.mail.outbox (as with Django's locmem backend).
+
+    In addition:
+    * Anymail send params parsed from the message will be attached to the outbox message
+      as a dict in the attr `anymail_test_params`
+    * If the caller supplies an `anymail_test_response` attr on the message, that will be
+      used instead of the default "sent" response. It can be either an AnymailRecipientStatus
+      or an instance of AnymailAPIError (or a subclass) to raise an exception.
     """
 
     esp_name = "Test"
 
     def __init__(self, *args, **kwargs):
-        # Init options from Django settings
-        esp_name = self.esp_name
-        self.sample_setting = get_anymail_setting('sample_setting', esp_name=esp_name,
-                                                  kwargs=kwargs, allow_bare=True)
-        self.recorded_send_params = get_anymail_setting('recorded_send_params', default=[],
-                                                        esp_name=esp_name, kwargs=kwargs)
         super(EmailBackend, self).__init__(*args, **kwargs)
+        if not hasattr(mail, 'outbox'):
+            mail.outbox = []  # see django.core.mail.backends.locmem
 
     def build_message_payload(self, message, defaults):
         return TestPayload(backend=self, message=message, defaults=defaults)
 
     def post_to_esp(self, payload, message):
-        # Keep track of the send params (for test-case access)
-        self.recorded_send_params.append(payload.params)
+        # Keep track of the sent messages and params (for test cases)
+        message.anymail_test_params = payload.params
+        mail.outbox.append(message)
         try:
             # Tests can supply their own message.test_response:
-            response = message.test_response
+            response = message.anymail_test_response
             if isinstance(response, AnymailAPIError):
                 raise response
         except AttributeError:
@@ -49,14 +54,6 @@ class EmailBackend(AnymailBaseBackend):
             raise AnymailAPIError('Unparsable test response')
 
 
-# Pre-v0.8 naming (immediately deprecated for this undocumented test feature)
-class TestBackend(object):
-    def __init__(self, **kwargs):
-        raise NotImplementedError(
-            "Anymail's (undocumented) TestBackend has been renamed to "
-            "'anymail.backends.test.EmailBackend'")
-
-
 class TestPayload(BasePayload):
     # For test purposes, just keep a dict of the params we've received.
     # (This approach is also useful for native API backends -- think of
@@ -129,3 +126,16 @@ class TestPayload(BasePayload):
     def set_esp_extra(self, extra):
         # Merge extra into params
         self.params.update(extra)
+
+
+class _EmailBackendWithRequiredSetting(EmailBackend):
+    """Test backend with a required setting `sample_setting`.
+
+    Intended only for internal use by Anymail settings tests.
+    """
+
+    def __init__(self, *args, **kwargs):
+        esp_name = self.esp_name
+        self.sample_setting = get_anymail_setting('sample_setting', esp_name=esp_name,
+                                                  kwargs=kwargs, allow_bare=True)
+        super(_EmailBackendWithRequiredSetting, self).__init__(*args, **kwargs)

docs/sending/anymail_additions.rst

@@ -218,11 +218,13 @@ ESP send status
     if you try to access it.
 
     This might cause problems in your test cases, because Django
-    `substitutes its own locmem email backend`_ during testing (so anymail_status
-    won't be set even after sending). Your code should either guard against
-    a missing anymail_status attribute, or use :class:`AnymailMessage`
-    (or the :class:`AnymailMessageMixin`) which initializes its anymail_status
-    attribute to a default AnymailStatus object.
+    :ref:`substitutes its own locmem EmailBackend <django:topics-testing-email>`
+    during testing (so anymail_status never gets attached to the EmailMessage).
+    If you run into this, you can: change your code to guard against
+    a missing anymail_status attribute; switch from using EmailMessage to
+    :class:`AnymailMessage` (or the :class:`AnymailMessageMixin`) to ensure the
+    anymail_status attribute is always there; or substitute
+    :ref:`Anymail's test backend <test-backend>` in any affected test cases.
 
     After sending through an Anymail backend,
     :attr:`~AnymailMessage.anymail_status` will be an object with these attributes:
@@ -321,10 +323,6 @@ ESP send status
             message.anymail_status.esp_response.json()
 
 
-.. _substitutes its own locmem email backend:
-   https://docs.djangoproject.com/en/stable/topics/testing/tools/#email-services
-
-
 .. _inline-images:
 
 Inline images

docs/tips/index.rst

@@ -10,6 +10,7 @@ done with Anymail:
    multiple_backends
    django_templates
    securing_webhooks
+   test_backend
 
 .. TODO:
 ..    Working with django-mailer(2)

docs/tips/test_backend.rst

@@ -0,0 +1,52 @@
+.. _test-backend:
+
+Testing your app
+================
+
+Django's own test runner makes sure your
+:ref:`test cases don't send email <django:topics-testing-email>`,
+by loading a dummy EmailBackend that accumulates messages
+in memory rather than sending them. That works just fine with Anymail.
+
+Anymail also includes its own "test" EmailBackend. This is intended primarily for
+Anymail's own internal tests, but you may find it useful for some of your test cases, too:
+
+* Like Django's locmem EmailBackend, Anymail's test EmailBackend collects sent messages
+  in :data:`django.core.mail.outbox`.
+  Django clears the outbox automatically between test cases.
+  See :ref:`email testing tools <django:topics-testing-email>` in the Django docs for more information.
+
+* Unlike the locmem backend, Anymail's test backend processes the messages as though they
+  would be sent by a generic ESP. This means every sent EmailMessage will end up with an
+  :attr:`~anymail.message.AnymailMessage.anymail_status` attribute after sending,
+  and some common problems like malformed addresses may be detected.
+  (But no ESP-specific checks are run.)
+
+* Anymail's test backend also adds an :attr:`anymail_send_params` attribute to each EmailMessage
+  as it sends it. This is a dict of the actual params that would be used to send the message,
+  including both Anymail-specific attributes from the EmailMessage and options that would
+  come from Anymail settings defaults.
+
+Here's an example:
+
+.. code-block:: python
+
+    from django.core import mail
+    from django.test import TestCase
+    from django.test.utils import override_settings
+
+    @override_settings(EMAIL_BACKEND='anymail.backends.test.EmailBackend')
+    class SignupTestCase(TestCase):
+        # Assume our app has a signup view that accepts an email address...
+        def test_sends_confirmation_email(self):
+            self.client.post("/account/signup/", {"email": "user@example.com"})
+
+            # Test that one message was sent:
+            self.assertEqual(len(mail.outbox), 1)
+
+            # Verify attributes of the EmailMessage that was sent:
+            self.assertEqual(mail.outbox[0].to, ["user@example.com"])
+            self.assertEqual(mail.outbox[0].tags, ["confirmation"])  # an Anymail custom attr
+
+            # Or verify the Anymail params, including any merged settings defaults:
+            self.assertTrue(mail.outbox[0].anymail_send_params["track_clicks"])

tests/test_general_backend.py

@@ -2,6 +2,7 @@ from datetime import datetime
 from email.mime.text import MIMEText
 
 import six
+from django.core import mail
 from django.core.exceptions import ImproperlyConfigured
 from django.core.mail import get_connection, send_mail
 from django.test import SimpleTestCase
@@ -16,34 +17,36 @@ from anymail.message import AnymailMessage
 from .utils import AnymailTestMixin
 
 
-recorded_send_params = []
-
-
-@override_settings(EMAIL_BACKEND='anymail.backends.test.EmailBackend',
-                   ANYMAIL_TEST_SAMPLE_SETTING='sample',  # required test EmailBackend setting
-                   ANYMAIL_TEST_RECORDED_SEND_PARAMS=recorded_send_params)
+@override_settings(EMAIL_BACKEND='anymail.backends.test.EmailBackend')
 class TestBackendTestCase(SimpleTestCase, AnymailTestMixin):
     """Base TestCase using Anymail's Test EmailBackend"""
 
     def setUp(self):
         super(TestBackendTestCase, self).setUp()
-        del recorded_send_params[:]  # empty the list from previous tests
         # Simple message useful for many tests
         self.message = AnymailMessage('Subject', 'Text Body', 'from@example.com', ['to@example.com'])
 
     @staticmethod
     def get_send_count():
         """Returns number of times "send api" has been called this test"""
-        return len(recorded_send_params)
+        try:
+            return len(mail.outbox)
+        except AttributeError:
+            return 0  # mail.outbox not initialized by either Anymail test or Django locmem backend
 
     @staticmethod
     def get_send_params():
         """Returns the params for the most recent "send api" call"""
-        return recorded_send_params[-1]
+        try:
+            return mail.outbox[-1].anymail_test_params
+        except IndexError:
+            raise IndexError("No messages have been sent through the Anymail test backend")
+        except AttributeError:
+            raise AttributeError("The last message sent was not processed through the Anymail test backend")
 
 
-@override_settings(EMAIL_BACKEND='anymail.backends.test.EmailBackend')  # but no ANYMAIL settings overrides
-class BackendSettingsTests(SimpleTestCase, AnymailTestMixin):           # (so not TestBackendTestCase)
+@override_settings(EMAIL_BACKEND='anymail.backends.test._EmailBackendWithRequiredSetting')
+class BackendSettingsTests(TestBackendTestCase):
     """Test settings initializations for Anymail EmailBackends"""
 
     @override_settings(ANYMAIL={'TEST_SAMPLE_SETTING': 'setting_from_anymail_settings'})

tests/test_send_signals.py

@@ -100,7 +100,7 @@ class TestPostSendSignal(TestBackendTestCase):
             self.receiver_called = True
         self.addCleanup(post_send.disconnect, receiver=handle_post_send)
 
-        self.message.test_response = {
+        self.message.anymail_test_response = {
             'recipient_status': {
                 'to@example.com': AnymailRecipientStatus(message_id=None, status='rejected')
             }