TASK: Document new test implementation

Documentation/source/extending.rst

@@ -55,6 +55,44 @@ a folder named like the sniff. E.g. you want to add a test for sniff
 :file:`src/Standards/Typo3Update/Sniffs/LegacyClassnames/DocCommentSniff.php`, the following folder
 has to exist: :file:`tests/Fixtures/Standards/Typo3Update/Sniffs/LegacyClassnames/DocCommentSniff/`.
 
+Also for convenience add a test class with following content:
+
+.. code-block:: php
+
+    <?php
+
+    namespace Typo3Update\Tests\Sniffs\Removed;
+
+    /*
+    * Copyright (C) 2017  Daniel Siepmann <coding@daniel-siepmann.de>
+    *
+    * 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 2
+    * 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, write to the Free Software
+    * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+    * 02110-1301, USA.
+    */
+
+    use Typo3Update\Tests\SniffsTest;
+
+    class TypoScriptSniffTest extends SniffsTest
+    {
+    }
+
+Place it accordingly to namespace. Adjust namespace and class name. No code is needed, everything is
+done in ``SniffsTest``. But this enables you to add ``--filter`` to ``phpunit`` to run just one
+test. Also IDEs support to run the single test file. This makes development much faster and failing
+tests more helpfull as they contain the class name.
+
 .. _extending-tests-single:
 
 Single test per sniff