test: add subclass example as unit test

redmail/test/email/test_cookbook.py

@@ -0,0 +1,45 @@
+
+from typing import Union
+from redmail import EmailSender
+
+def test_distributions():
+    class DistrSender(EmailSender):
+        "Send email using pre-defined distribution lists"
+
+        def __init__(self, *args, distribution:dict, **kwargs):
+            super().__init__(*args, **kwargs)
+            self.distributions = distribution
+
+        def get_receivers(self, receiver_list):
+            if receiver_list:
+                return self.distributions[receiver_list]
+
+        def get_cc(self, receiver_list):
+            if receiver_list:
+                return self.distributions[receiver_list]
+
+        def get_bcc(self, receiver_list):
+            if receiver_list:
+                return self.distributions[receiver_list]
+
+    email = DistrSender(
+        host="localhost", 
+        port=0,
+        distribution={
+            'group1': ["me@example.com", "you@example.com"],
+            'group2': ["he@example.com", "she@example.com"],
+        }
+    )
+
+    msg = email.get_message(
+        sender="me@example.com",
+        receivers="group1",
+        cc="group2",
+        subject="Some email",
+    )
+    assert dict(msg.items()) == {
+        'from': 'me@example.com', 
+        'subject': 'Some email', 
+        'to': 'me@example.com, you@example.com', 
+        'cc': 'he@example.com, she@example.com', 
+    }