Add license header to test files

tests/test_core_tokenizer.py

@@ -1,5 +1,23 @@
 # -*- coding: utf-8 -*-
-"""novelWriter Tokenizer Class Tester
+"""
+novelWriter – Tokenizer Class Tester
+====================================
+
+This file is a part of novelWriter
+Copyright 2018–2021, Veronica Berglyd Olsen
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <https://www.gnu.org/licenses/>.
 """
 
 import pytest