diff --git a/test/test_utils.py b/test/test_utils.py
index b3de14198..7bab7ff05 100644
--- a/test/test_utils.py
+++ b/test/test_utils.py
@@ -3,19 +3,20 @@
 # Allow direct execution
 import os
 import sys
-import unittest
-import unittest.mock
-import warnings
-import datetime as dt
 
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 
 
 import contextlib
+import datetime as dt
 import io
 import itertools
 import json
+import pickle
 import subprocess
+import unittest
+import unittest.mock
+import warnings
 import xml.etree.ElementTree
 
 from yt_dlp.compat import (
@@ -2068,21 +2069,26 @@ def test_http_header_dict(self):
         headers = HTTPHeaderDict()
         headers['ytdl-test'] = b'0'
         self.assertEqual(list(headers.items()), [('Ytdl-Test', '0')])
+        self.assertEqual(list(headers.sensitive().items()), [('ytdl-test', '0')])
         headers['ytdl-test'] = 1
         self.assertEqual(list(headers.items()), [('Ytdl-Test', '1')])
+        self.assertEqual(list(headers.sensitive().items()), [('ytdl-test', '1')])
         headers['Ytdl-test'] = '2'
         self.assertEqual(list(headers.items()), [('Ytdl-Test', '2')])
+        self.assertEqual(list(headers.sensitive().items()), [('Ytdl-test', '2')])
         self.assertTrue('ytDl-Test' in headers)
         self.assertEqual(str(headers), str(dict(headers)))
         self.assertEqual(repr(headers), str(dict(headers)))
 
         headers.update({'X-dlp': 'data'})
         self.assertEqual(set(headers.items()), {('Ytdl-Test', '2'), ('X-Dlp', 'data')})
+        self.assertEqual(set(headers.sensitive().items()), {('Ytdl-test', '2'), ('X-dlp', 'data')})
         self.assertEqual(dict(headers), {'Ytdl-Test': '2', 'X-Dlp': 'data'})
         self.assertEqual(len(headers), 2)
         self.assertEqual(headers.copy(), headers)
-        headers2 = HTTPHeaderDict({'X-dlp': 'data3'}, **headers, **{'X-dlp': 'data2'})
+        headers2 = HTTPHeaderDict({'X-dlp': 'data3'}, headers, **{'X-dlP': 'data2'})
         self.assertEqual(set(headers2.items()), {('Ytdl-Test', '2'), ('X-Dlp', 'data2')})
+        self.assertEqual(set(headers2.sensitive().items()), {('Ytdl-test', '2'), ('X-dlP', 'data2')})
         self.assertEqual(len(headers2), 2)
         headers2.clear()
         self.assertEqual(len(headers2), 0)
@@ -2090,16 +2096,23 @@ def test_http_header_dict(self):
         # ensure we prefer latter headers
         headers3 = HTTPHeaderDict({'Ytdl-TeSt': 1}, {'Ytdl-test': 2})
         self.assertEqual(set(headers3.items()), {('Ytdl-Test', '2')})
+        self.assertEqual(set(headers3.sensitive().items()), {('Ytdl-test', '2')})
         del headers3['ytdl-tesT']
         self.assertEqual(dict(headers3), {})
 
         headers4 = HTTPHeaderDict({'ytdl-test': 'data;'})
         self.assertEqual(set(headers4.items()), {('Ytdl-Test', 'data;')})
+        self.assertEqual(set(headers4.sensitive().items()), {('ytdl-test', 'data;')})
 
         # common mistake: strip whitespace from values
         # https://github.com/yt-dlp/yt-dlp/issues/8729
         headers5 = HTTPHeaderDict({'ytdl-test': ' data; '})
         self.assertEqual(set(headers5.items()), {('Ytdl-Test', 'data;')})
+        self.assertEqual(set(headers5.sensitive().items()), {('ytdl-test', 'data;')})
+
+        # test if picklable
+        headers6 = HTTPHeaderDict(a=1, b=2)
+        self.assertEqual(pickle.loads(pickle.dumps(headers6)), headers6)
 
     def test_extract_basic_auth(self):
         assert extract_basic_auth('http://:foo.bar') == ('http://:foo.bar', None)