fix: Add username generation tests and utility functions

- Introduced `remove_special_characters_from_name` and `generate_username_suggestions` functions to enhance username handling.
- Added comprehensive test cases for username generation, including ASCII validation and uniqueness checks.
- Implemented tests for special character removal and suggestion generation based on various input scenarios, including edge cases.

openedx/core/djangoapps/user_authn/tests/test_utils.py

@@ -9,7 +9,11 @@ from django.test.client import RequestFactory
 from django.test.utils import override_settings
 
 from openedx.core.djangoapps.oauth_dispatch.tests.factories import ApplicationFactory
-from openedx.core.djangoapps.user_authn.utils import is_safe_login_or_logout_redirect
+from openedx.core.djangoapps.user_authn.utils import (
+    is_safe_login_or_logout_redirect,
+    generate_username_suggestions,
+    remove_special_characters_from_name,
+)
 
 
 @ddt.ddt
@@ -68,3 +72,73 @@ class TestRedirectUtils(TestCase):
         req = self.request.get(f'/logout?{urlencode(params)}', HTTP_HOST=host)
         actual_is_safe = self._is_safe_redirect(req, redirect_url)
         assert actual_is_safe == expected_is_safe
+
+
+@ddt.ddt
+class TestUsernameGeneration(TestCase):
+    """Test username generation utility methods."""
+
+    def test_remove_special_characters(self):
+        """Test the removal of special characters from a name."""
+        test_cases = [
+            ('John Doe', 'JohnDoe'),
+            ('John@Doe', 'JohnDoe'),
+            ('John.Doe', 'JohnDoe'),
+            ('John_Doe', 'John_Doe'),  # Underscore is allowed
+            ('John-Doe', 'John-Doe'),  # Hyphen is allowed
+            ('John$#@!Doe', 'JohnDoe'),
+        ]
+        for input_name, expected in test_cases:
+            assert remove_special_characters_from_name(input_name) == expected
+
+    @ddt.data(
+        # Test normal ASCII name
+        ('John Doe', True),  # Should return suggestions
+        ('Jane Smith', True),  # Should return suggestions
+        # Test non-ASCII names
+        ('José García', False),  # Contains non-ASCII characters
+        ('مریم میرزاخانی', False),  # Persian name
+        ('明美 田中', False),  # Japanese name
+        ('Σωκράτης', False),  # Greek name
+        ('Владимир', False),  # Cyrillic characters
+        # Test edge cases
+        ('A B', True),  # Minimal valid name
+        ('', True),  # Empty string
+        ('   ', True),  # Just spaces
+    )
+    @ddt.unpack
+    def test_username_suggestions_ascii_check(self, name, should_generate):
+        """Test username suggestion generation for ASCII and non-ASCII names."""
+        suggestions = generate_username_suggestions(name)
+
+        if should_generate:
+            if name.strip():  # If name is not empty or just spaces
+                # Should generate up to 3 suggestions for valid ASCII names
+                assert len(suggestions) <= 3
+                # Verify all suggestions are ASCII
+                for suggestion in suggestions:
+                    assert suggestion.isascii()
+                    assert suggestion.replace('_', '').replace('-', '').isalnum()
+            else:
+                # Empty or whitespace-only names should return empty list
+                assert not suggestions
+        else:
+            # Should return empty list for non-ASCII names
+            assert not suggestions
+
+    def test_unique_suggestions(self):
+        """Test that generated suggestions are unique."""
+        name = "John Doe"
+        suggestions = generate_username_suggestions(name)
+        assert len(suggestions) == len(set(suggestions)), "All suggestions should be unique"
+
+    def test_suggestion_length(self):
+        """Test that generated suggestions respect the maximum length."""
+        from openedx.core.djangoapps.user_api.accounts import USERNAME_MAX_LENGTH
+
+        # Test with a very long name
+        long_name = "John" * 50
+        suggestions = generate_username_suggestions(long_name)
+
+        for suggestion in suggestions:
+            assert len(suggestion) <= USERNAME_MAX_LENGTH