diff --git a/tests/__init__.py b/tests/__init__.py
index 40a96af..7934bb2 100644
--- a/tests/__init__.py
+++ b/tests/__init__.py
@@ -1 +1,3 @@
 # -*- coding: utf-8 -*-
+# This file is under GNU Affero General Public License 3.0
+# see LICENSE.txt
diff --git a/tests/conftest.py b/tests/conftest.py
index d687614..71bd834 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,4 +1,7 @@
 # -*- coding: utf-8 -*-
+# This file is under GNU Affero General Public License 3.0
+# see LICENSE.txt
+
 """pytest configuration for the unit tests."""
 
 from .model import *
diff --git a/tests/constants.py b/tests/constants.py
index 77f6157..a141ea6 100644
--- a/tests/constants.py
+++ b/tests/constants.py
@@ -1,4 +1,7 @@
 # -*- coding: utf-8 -*-
+# This file is under GNU Affero General Public License 3.0
+# see LICENSE.txt
+
 """Constants for unit tests."""
 DATADIR = "data"
 
diff --git a/tests/model.py b/tests/model.py
index d2d9aa3..28bf5a2 100644
--- a/tests/model.py
+++ b/tests/model.py
@@ -1,4 +1,8 @@
-from . import utils
+# -*- coding: utf-8 -*-
+# This file is under GNU Affero General Public License 3.0
+# see LICENSE.txt
+
+# from . import utils
 
 import pytest
 
diff --git a/tests/test_basic.py b/tests/test_basic.py
index dca161b..3b1cacf 100644
--- a/tests/test_basic.py
+++ b/tests/test_basic.py
@@ -1,5 +1,6 @@
-#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
+# This file is under GNU Affero General Public License 3.0
+# see LICENSE.txt
 
 # from . import constants
 import pytest
diff --git a/tests/test_identity.py b/tests/test_identity.py
index 3e044ff..62125b6 100644
--- a/tests/test_identity.py
+++ b/tests/test_identity.py
@@ -1,4 +1,7 @@
 # -*- coding: utf-8 -*-
+# This file is under GNU Affero General Public License 3.0
+# see LICENSE.txt
+
 """Identity unit tests."""
 
 import pytest
diff --git a/tests/test_message.py b/tests/test_message.py
index e527206..58b99f2 100644
--- a/tests/test_message.py
+++ b/tests/test_message.py
@@ -1,4 +1,7 @@
 # -*- coding: utf-8 -*-
+# This file is under GNU Affero General Public License 3.0
+# see LICENSE.txt
+
 """Message unit tests."""
 
 from . import constants
diff --git a/tests/test_pep.py b/tests/test_pep.py
index 976c74f..75a5222 100755
--- a/tests/test_pep.py
+++ b/tests/test_pep.py
@@ -1,4 +1,7 @@
 # -*- coding: utf-8 -*-
+# This file is under GNU Affero General Public License 3.0
+# see LICENSE.txt
+
 """Unit test for pEp package, not for subpackages or modules."""
 
 
diff --git a/tests/utils.py b/tests/utils.py
index 008978b..931ead0 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -1,4 +1,8 @@
-from . import constants
+# -*- coding: utf-8 -*-
+# This file is under GNU Affero General Public License 3.0
+# see LICENSE.txt
+
+# from . import constants
 
 import pathlib
 
diff --git a/utils/pEp b/utils/pEp
index 086eff0..1710163 100755
--- a/utils/pEp
+++ b/utils/pEp
@@ -1,5 +1,7 @@
 #!/usr/bin/env python3
 # -*- coding: utf-8 -*-
+# This file is under GNU Affero General Public License 3.0
+# see LICENSE.txt
 
 
 """