diff --git a/test/test_oauth.py b/test/test_oauth.py
index 7455928d..0082419d 100644
--- a/test/test_oauth.py
+++ b/test/test_oauth.py
@@ -1,7 +1,7 @@
 #!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
-# Copyright 2018-2020 Mike Fährmann
+# Copyright 2018-2023 Mike Fährmann
 #
 # This program is free software; you can redistribute it and/or modify
 # it under the terms of the GNU General Public License version 2 as
@@ -10,6 +10,7 @@
 import os
 import sys
 import unittest
+from unittest.mock import patch
 
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 from gallery_dl import oauth, text  # noqa E402
@@ -66,6 +67,53 @@ class TestOAuthSession(unittest.TestCase):
             self.assertTrue(len(quoted) >= 3)
             self.assertEqual(quoted_hex.upper(), quoted_hex)
 
+    def test_generate_signature(self):
+        client = oauth.OAuth1Client(
+            CONSUMER_KEY, CONSUMER_SECRET, ACCESS_TOKEN, ACCESS_TOKEN_SECRET)
+
+        request = MockRequest()
+        params = []
+        self.assertEqual(
+            client.generate_signature(request, params),
+            "Wt2xo49dM5pkL4gsnCakNdHaVUo%3D")
+
+        request = MockRequest("https://example.org/")
+        params = [("hello", "world"), ("foo", "bar")]
+        self.assertEqual(
+            client.generate_signature(request, params),
+            "ay2269%2F8uKpZqKJR1doTtpv%2Bzn0%3D")
+
+        request = MockRequest("https://example.org/index.html"
+                              "?hello=world&foo=bar", method="POST")
+        params = [("oauth_signature_method", "HMAC-SHA1")]
+        self.assertEqual(
+            client.generate_signature(request, params),
+            "yVZWb1ts4smdMmXxMlhaXrkoOng%3D")
+
+    def test_dunder_call(self):
+        client = oauth.OAuth1Client(
+            CONSUMER_KEY, CONSUMER_SECRET, ACCESS_TOKEN, ACCESS_TOKEN_SECRET)
+        request = MockRequest("https://example.org/")
+
+        with patch("time.time") as tmock, \
+             patch("gallery_dl.oauth.nonce") as nmock:
+            tmock.return_value = 123456789.123
+            nmock.return_value = "abcdefghijklmno"
+
+            client(request)
+
+        self.assertEqual(
+            request.headers["Authorization"],
+            """OAuth \
+oauth_consumer_key="key",\
+oauth_nonce="abcdefghijklmno",\
+oauth_signature_method="HMAC-SHA1",\
+oauth_timestamp="123456789",\
+oauth_version="1.0",\
+oauth_token="accesskey",\
+oauth_signature="DjtTk5j5P3BDZFnstZ%2FtEYcwD6c%3D"\
+""")
+
     def test_request_token(self):
         response = self._oauth_request(
             "/request_token.php", {})
@@ -110,5 +158,13 @@ class TestOAuthSession(unittest.TestCase):
             raise unittest.SkipTest()
 
 
+class MockRequest():
+
+    def __init__(self, url="", method="GET"):
+        self.url = url
+        self.method = method
+        self.headers = {}
+
+
 if __name__ == "__main__":
     unittest.main(warnings="ignore")