Add regression checks on email validator.

This is mostly to ensure that it rejects domains (other than
"localhost") without dots in them.

pyproject.toml

@@ -46,7 +46,7 @@ exclude_dirs = ["src/django_registration/_backports.py"]
 skips = ["B101"]
 
 [tool.black]
-target-version = ["py38", "py39", "py310", "py311", "py312"]
+target-version = ["py39", "py310", "py311", "py312", "py313"]
 
 [tool.check-manifest]
 ignore-bad-ideas = ["*.mo"]
@@ -114,6 +114,3 @@ disable = [
   "missing-module-docstring",
   "too-many-ancestors",
 ]
-
-[dependency-groups]
-tests = ["nox"]

src/django_registration/validators.py

@@ -39,7 +39,6 @@
     r"(?:[a-zA-Z0-9-]{0,61}[a-zA-Z0-9])?)*$"
 )
 
-
 # Below we construct a large but non-exhaustive list of names which users probably
 # should not be able to register with, due to various risks:
 #
@@ -67,7 +66,6 @@
     "wpad",  # Proxy autodiscovery
 ]
 
-
 PROTOCOL_HOSTNAMES = [
     # Common protocol hostnames.
     "ftp",
@@ -83,7 +81,6 @@
     "www",
 ]
 
-
 CA_ADDRESSES = [
     # Email addresses known used by certificate authorities during
     # verification.
@@ -103,7 +100,6 @@
     "webmaster",
 ]
 
-
 RFC_2142 = [
     # RFC-2142-defined names not already covered.
     "abuse",
@@ -114,7 +110,6 @@
     "support",
 ]
 
-
 NOREPLY_ADDRESSES = [
     # Common no-reply email addresses.
     "mailer-daemon",
@@ -123,7 +118,6 @@
     "no-reply",
 ]
 
-
 SENSITIVE_FILENAMES = [
     # Sensitive filenames.
     "clientaccesspolicy.xml",  # Silverlight cross-domain policy file.
@@ -136,7 +130,6 @@
     ".htpasswd",
 ]
 
-
 OTHER_SENSITIVE_NAMES = [
     # Other names which could be problems depending on URL/subdomain
     # structure.
@@ -194,7 +187,6 @@
     "xrpc",  # Used by Bluesky/AT protocol for domain verification.
 ]
 
-
 DEFAULT_RESERVED_NAMES = (
     SPECIAL_HOSTNAMES
     + PROTOCOL_HOSTNAMES

tests/test_forms.py

@@ -49,25 +49,30 @@ def test_email_validation(self):
             "[email protected]",
             "[email protected]",
             "[email protected]",
+            "test@localhost",  # Django's default validator allows this one.
         ):
-            user_data = self.valid_data.copy()
-            user_data["email"] = value
-            form = forms.RegistrationForm(data=user_data)
-            assert form.is_valid()
+            with self.subTest(value=value):
+                user_data = self.valid_data.copy()
+                user_data["email"] = value
+                form = forms.RegistrationForm(data=user_data)
+                assert form.is_valid()
         for value in (
             "@@@example.com",
             "test:test@[email protected]",
             'test"test@example"[email protected]',
+            "test@example",
+            "test@1234",
         ):
-            user_data = self.valid_data.copy()
-            user_data["email"] = value
-            form = forms.RegistrationForm(data=user_data)
-            assert not form.is_valid()
-            assert form.has_error(user_model.get_email_field_name())
-            assert (
-                str(validators.HTML5EmailValidator.message)
-                in form.errors[user_model.get_email_field_name()]
-            )
+            with self.subTest(value=value):
+                user_data = self.valid_data.copy()
+                user_data["email"] = value
+                form = forms.RegistrationForm(data=user_data)
+                assert not form.is_valid()
+                assert form.has_error(user_model.get_email_field_name())
+                assert (
+                    str(validators.HTML5EmailValidator.message)
+                    in form.errors[user_model.get_email_field_name()]
+                )
 
     def test_email_validated_once(self):
         """