Add unit tests for generate_api_token function

Enhance the coverage and robustness of the `generate_api_token` helper
in `app/api/api_tokens.py` by introducing three unit tests.

The new tests verify:
- The exact character length of the generated string based on `TOKEN_BYTES`.
- The character set strictly adheres to URL-safe characters and the expected `TOKEN_PREFIX`.
- `secrets.token_urlsafe` is explicitly called with `TOKEN_BYTES`.

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

tests/test_api_tokens.py

@@ -534,6 +534,42 @@ class TestTokenUtils:
         tokens = {generate_api_token() for _ in range(100)}
         assert len(tokens) == 100
 
+    @pytest.mark.unit
+    def test_generate_api_token_length(self):
+        """Generated tokens should have the exact expected length based on TOKEN_BYTES."""
+        import math
+        from app.api.api_tokens import generate_api_token, TOKEN_PREFIX, TOKEN_BYTES
+
+        # base64url encoding of N bytes without padding: ceil(N * 4 / 3) characters
+        expected_b64_len = math.ceil(TOKEN_BYTES * 4 / 3)
+        expected_total_len = len(TOKEN_PREFIX) + expected_b64_len
+
+        token = generate_api_token()
+        assert len(token) == expected_total_len
+
+    @pytest.mark.unit
+    def test_generate_api_token_charset(self):
+        """Generated tokens should only contain URL-safe base64 characters and the prefix."""
+        import re
+        from app.api.api_tokens import generate_api_token, TOKEN_PREFIX
+
+        token = generate_api_token()
+        # Check it starts with prefix and the rest is base64url chars ([A-Za-z0-9_-])
+        pattern = f"^{re.escape(TOKEN_PREFIX)}[A-Za-z0-9_\\-]+$"
+        assert re.match(pattern, token) is not None
+
+    @pytest.mark.unit
+    def test_generate_api_token_uses_secrets(self):
+        """Generated tokens should use secrets.token_urlsafe with the correct number of bytes."""
+        from unittest.mock import patch
+        from app.api.api_tokens import generate_api_token, TOKEN_BYTES, TOKEN_PREFIX
+
+        with patch("app.api.api_tokens.secrets.token_urlsafe", return_value="mocked_token") as mock_secrets:
+            token = generate_api_token()
+            mock_secrets.assert_called_once_with(TOKEN_BYTES)
+            assert token == f"{TOKEN_PREFIX}mocked_token"
+
+
     @pytest.mark.unit
     def test_hash_token_deterministic(self):
         """Hashing the same token should always produce the same result."""