Idea for using composition rather than inheritance

tests/utils/test_mailer.py

@@ -1,44 +1,40 @@
 import pytest
-from atst.utils.mailer import Mailer, RedisMailer
+from atst.utils.mailer import Mailer, Mailer, MailConnection, RedisConnection
 
 
-class MockHost:
+class MockConnection(MailConnection):
     def __init__(self):
-        self.messages = []
+        self._messages = []
 
-    def __enter__(self):
-        return self
+    def send(self, message):
+        self._messages.append(message)
 
-    def __exit__(self, *args):
-        pass
-
-    def send_message(self, message):
-        self.messages.append(message)
+    @property
+    def messages(self):
+        return self._messages
 
 
 @pytest.fixture
-def mail_host():
-    return MockHost()
+def mailer():
+    return Mailer(MockConnection(), "test@atat.com")
 
 
-def test_mailer_can_send_mail(monkeypatch, mail_host):
-    monkeypatch.setattr("atst.utils.mailer.Mailer.connection", lambda *args: mail_host)
-    mailer = Mailer("localhost", 456, "leia@rebellion.net", "droidsyourelookingfor")
+def test_mailer_can_send_mail(mailer):
     message_data = {
         "recipients": ["ben@tattoine.org"],
         "subject": "help",
         "body": "you're my only hope",
     }
     mailer.send(**message_data)
-    assert len(mail_host.messages) == 1
-    message = mail_host.messages[0]
+    assert len(mailer.messages) == 1
+    message = mailer.messages[0]
     assert message["To"] == message_data["recipients"][0]
     assert message["Subject"] == message_data["subject"]
     assert message.get_content().strip() == message_data["body"]
 
 
 def test_redis_mailer_can_save_messages(app):
-    mailer = RedisMailer(app.redis, server=None, port=None, sender=None, password=None)
+    mailer = Mailer(RedisConnection(app.redis), "test@atat.com")
     message_data = {
         "recipients": ["ben@tattoine.org"],
         "subject": "help",