Raise error for invalidly-formatted email addresses.

A message's `from_email` and each address in its `to`, `cc`, and `bcc` lists must contain exactly one email address. Previous code would silently ignore additional addresses, leading to unusual behavior. Now, raises new `AnymailInvalidAddress` exception.

Example: `from_email='Widgets, Inc. <widgets@example.com>'` is invalid: it needs double-quotes around the "Widgets, Inc." display-name portion. In earlier versions, this probably would have sent the message from something like "From: Widgets <@localhost>". Now, it will raise an exception.

**Potentially-breaking change:** If your code is using an unquoted display-name containing a comma in an email address, it will now raise an error. In earlier versions, this may have appeared to succeed, but was almost certainly not doing what you intended.

Fixes #44.

tests/test_utils.py

@@ -0,0 +1,63 @@
+# Tests for the anymail/utils.py module
+# (not to be confused with utilities for testing found in in tests/utils.py)
+
+from django.test import SimpleTestCase
+
+from anymail.exceptions import AnymailInvalidAddress
+from anymail.utils import ParsedEmail
+
+
+class ParsedEmailTests(SimpleTestCase):
+    """Test utils.ParsedEmail"""
+
+    # Anymail (and Djrill) have always used EmailMessage.encoding, which defaults to None.
+    # (Django substitutes settings.DEFAULT_ENCODING='utf-8' when converting to a mime message,
+    # but Anymail has never used that code.)
+    ADDRESS_ENCODING = None
+
+    def test_simple_email(self):
+        parsed = ParsedEmail("test@example.com", self.ADDRESS_ENCODING)
+        self.assertEqual(parsed.email, "test@example.com")
+        self.assertEqual(parsed.name, "")
+        self.assertEqual(parsed.address, "test@example.com")
+
+    def test_display_name(self):
+        parsed = ParsedEmail('"Display Name, Inc." <test@example.com>', self.ADDRESS_ENCODING)
+        self.assertEqual(parsed.email, "test@example.com")
+        self.assertEqual(parsed.name, "Display Name, Inc.")
+        self.assertEqual(parsed.address, '"Display Name, Inc." <test@example.com>')
+
+    def test_obsolete_display_name(self):
+        # you can get away without the quotes if there are no commas or parens
+        # (but it's not recommended)
+        parsed = ParsedEmail('Display Name <test@example.com>', self.ADDRESS_ENCODING)
+        self.assertEqual(parsed.email, "test@example.com")
+        self.assertEqual(parsed.name, "Display Name")
+        self.assertEqual(parsed.address, 'Display Name <test@example.com>')
+
+    def test_unicode_display_name(self):
+        parsed = ParsedEmail(u'"Unicode \N{HEAVY BLACK HEART}" <test@example.com>', self.ADDRESS_ENCODING)
+        self.assertEqual(parsed.email, "test@example.com")
+        self.assertEqual(parsed.name, u"Unicode \N{HEAVY BLACK HEART}")
+        # display-name automatically shifts to quoted-printable/base64 for non-ascii chars:
+        self.assertEqual(parsed.address, '=?utf-8?b?VW5pY29kZSDinaQ=?= <test@example.com>')
+
+    def test_invalid_display_name(self):
+        with self.assertRaises(AnymailInvalidAddress):
+            # this parses as multiple email addresses, because of the comma:
+            ParsedEmail('Display Name, Inc. <test@example.com>', self.ADDRESS_ENCODING)
+
+    def test_none_address(self):
+        # used for, e.g., telling Mandrill to use template default from_email
+        parsed = ParsedEmail(None, self.ADDRESS_ENCODING)
+        self.assertEqual(parsed.email, None)
+        self.assertEqual(parsed.name, None)
+        self.assertEqual(parsed.address, None)
+
+    def test_empty_address(self):
+        with self.assertRaises(AnymailInvalidAddress):
+            ParsedEmail('', self.ADDRESS_ENCODING)
+
+    def test_whitespace_only_address(self):
+        with self.assertRaises(AnymailInvalidAddress):
+            ParsedEmail(' ', self.ADDRESS_ENCODING)