diff --git a/tests/test_util.py b/tests/test_util.py
new file mode 100644
index 0000000..3e804f8
--- /dev/null
+++ b/tests/test_util.py
@@ -0,0 +1,75 @@
+# SPDX-License-Identifier: MIT
+#
+# Copyright (c) 2017 PySecretHandshake contributors (see AUTHORS for more details)
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the "Software"), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+
+"""Tests for utility functions"""
+
+import math
+
+import pytest
+
+from secret_handshake.util import bytes_to_long, long_to_bytes
+
+
+@pytest.mark.parametrize(
+    "in_,out",
+    (
+        (0, b"\x00"),
+        (1, b"\x01"),
+        (4278255360, b"\xff\x00\xff\x00"),
+        (65536, b"\x01\x00\x00"),
+        (4546694913, b"\x01\x0f\x01\x0f\x01"),
+    ),
+)
+@pytest.mark.parametrize("blocksize", (0, 4, 6))
+def test_long_to_bytes(in_: int, out: bytes, blocksize: int) -> None:
+    """Test long_to_bytes"""
+
+    result = long_to_bytes(in_, blocksize=blocksize)
+
+    if blocksize:
+        block_count = math.ceil(len(out) / blocksize)
+    else:
+        block_count = 1
+
+    padding = b"\x00" * blocksize * block_count
+    expected = (padding + out)[-(blocksize * block_count) :]
+
+    if blocksize:
+        assert not len(result) % blocksize
+
+    assert result == expected
+
+
+@pytest.mark.parametrize(
+    "in_,out",
+    (
+        (b"\x00\x00\x00\x00", 0),
+        (b"\x00\x00\x00\x01", 1),
+        (b"\xff\x00\xff\x00", 4278255360),
+        (b"\x01\x00\x00", 65536),
+        (b"\x01\x0f\x01\x0f\x01", 4546694913),
+    ),
+)
+def test_bytes_to_long(in_: bytes, out: int) -> None:
+    """Test bytes_to_long"""
+
+    assert bytes_to_long(in_) == out