diff --git a/test/string_test.py b/test/string_test.py
index 2c4e943f..742fb854 100644
--- a/test/string_test.py
+++ b/test/string_test.py
@@ -10,34 +10,34 @@ class TestString(unittest.TestCase):
 
     # pylint: disable=too-many-public-methods,invalid-name
 
-    def test_encoding(self):
+    def test_encoding(self) -> None:
         """Test simple encoding."""
         self.assertEqual(string_to_bytes("fnord", 10), b"fnord" + bytes(5))
 
-    def test_encoding_without_padding(self):
+    def test_encoding_without_padding(self) -> None:
         """Test encoding with exact match of size."""
         self.assertEqual(string_to_bytes("fnord", 5), b"fnord")
 
-    def test_encoding_failure(self):
+    def test_encoding_failure(self) -> None:
         """Test error while encoding."""
         with self.assertRaises(PyVLXException):
             string_to_bytes("fnord", 4)
 
-    def test_decoding(self):
+    def test_decoding(self) -> None:
         """Test decoding of string."""
         self.assertEqual(bytes_to_string(b"fnord" + bytes(5)), "fnord")
 
-    def test_decoding_without_padding(self):
+    def test_decoding_without_padding(self) -> None:
         """Test decoding of string without padding."""
         self.assertEqual(bytes_to_string(b"fnord"), "fnord")
 
-    def test_encode_utf8(self):
+    def test_encode_utf8(self) -> None:
         """Test encoding a string with special characters."""
         self.assertEqual(
             string_to_bytes("Fenster Büro", 16), b"Fenster B\xc3\xbcro\x00\x00\x00"
         )
 
-    def test_decode_utf8(self):
+    def test_decode_utf8(self) -> None:
         """Test decoding a string with special characters."""
         self.assertEqual(
             bytes_to_string(b"Fenster B\xc3\xbcro\x00\x00\x00"), "Fenster Büro"