Add send-template tests (and fixes).

Add test cases for send-template.
Expand template_content dict into Mandrill's name/value array.
Don't send template_content as "None" if missing.

Clean up some variable names in the backend.

djrill/tests/test_mandrill_send_template.py

@@ -0,0 +1,50 @@
+from django.core import mail
+
+from djrill.tests.mock_backend import DjrillBackendMockAPITestCase
+
+
+class DjrillMandrillSendTemplateTests(DjrillBackendMockAPITestCase):
+    """Test Djrill backend support for Mandrill send-template features"""
+
+    def test_send_template(self):
+        msg = mail.EmailMessage('Subject', 'Text Body',
+            'from@example.com', ['to@example.com'])
+        msg.template_name = "PERSONALIZED_SPECIALS"
+        msg.template_content = {
+            'HEADLINE': "<h1>Specials Just For *|FNAME|*</h1>",
+            'OFFER_BLOCK': "<p><em>Half off</em> all fruit</p>"
+        }
+        msg.send()
+        self.assert_mandrill_called("/messages/send-template.json")
+        data = self.get_api_call_data()
+        self.assertEqual(data['template_name'], "PERSONALIZED_SPECIALS")
+        # Djrill expands simple python dicts into the more-verbose name/value
+        # structures the Mandrill API uses
+        self.assertEqual(data['template_content'],
+            [ {'name': "HEADLINE",
+               'value': "<h1>Specials Just For *|FNAME|*</h1>"},
+              {'name': "OFFER_BLOCK",
+               'value': "<p><em>Half off</em> all fruit</p>"} ]
+        )
+
+    def test_no_template_content(self):
+        # Just a template, without any template_content to be merged
+        msg = mail.EmailMessage('Subject', 'Text Body',
+            'from@example.com', ['to@example.com'])
+        msg.template_name = "WELCOME_MESSAGE"
+        msg.send()
+        self.assert_mandrill_called("/messages/send-template.json")
+        data = self.get_api_call_data()
+        self.assertEqual(data['template_name'], "WELCOME_MESSAGE")
+        self.assertFalse('template_content' in data)
+
+    def test_non_template_send(self):
+        # Make sure the non-template case still uses /messages/send.json
+        msg = mail.EmailMessage('Subject', 'Text Body',
+            'from@example.com', ['to@example.com'])
+        msg.send()
+        self.assert_mandrill_called("/messages/send.json")
+        data = self.get_api_call_data()
+        self.assertFalse('template_name' in data)
+        self.assertFalse('template_content' in data)
+        self.assertFalse('async' in data)