Add missing license header.
diff --git a/tests/hypothesis/test_fernet.py b/tests/hypothesis/test_fernet.py
index fd24380..c652869 100644
--- a/tests/hypothesis/test_fernet.py
+++ b/tests/hypothesis/test_fernet.py
@@ -1,3 +1,7 @@
+# This file is dual licensed under the terms of the Apache License, Version
+# 2.0, and the BSD License. See the LICENSE file in the root of this repository
+# for complete details.
+
 from hypothesis import given
 from hypothesis.strategies import binary