Fixed #21379 -- Created auth-specific username validators

Thanks Tim Graham for the review.

tests/auth_tests/test_validators.py

@@ -1,7 +1,9 @@
+# -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
 import os
 
+from django.contrib.auth import validators
 from django.contrib.auth.models import User
 from django.contrib.auth.password_validation import (
     CommonPasswordValidator, MinimumLengthValidator, NumericPasswordValidator,
@@ -174,3 +176,29 @@ class NumericPasswordValidatorTest(TestCase):
             NumericPasswordValidator().get_help_text(),
             "Your password can't be entirely numeric."
         )
+
+
+class UsernameValidatorsTests(TestCase):
+    def test_unicode_validator(self):
+        valid_usernames = ['joe', 'René', 'ᴮᴵᴳᴮᴵᴿᴰ', 'أحمد']
+        invalid_usernames = [
+            "o'connell", "عبد ال",
+            "zerowidth\u200Bspace", "nonbreaking\u00A0space",
+            "en\u2013dash",
+        ]
+        v = validators.UnicodeUsernameValidator()
+        for valid in valid_usernames:
+            v(valid)
+        for invalid in invalid_usernames:
+            with self.assertRaises(ValidationError):
+                v(invalid)
+
+    def test_ascii_validator(self):
+        valid_usernames = ['glenn', 'GLEnN', 'jean-marc']
+        invalid_usernames = ["o'connell", 'Éric', 'jean marc', "أحمد"]
+        v = validators.ASCIIUsernameValidator()
+        for valid in valid_usernames:
+            v(valid)
+        for invalid in invalid_usernames:
+            with self.assertRaises(ValidationError):
+                v(invalid)