Add testing instructions to README.md.

README.md

@@ -31,3 +31,66 @@ Contributors
 - Daniel Kraus (@bovender), main developer
 - Ulrich Strauss (@c0nnex), namespaces
 - Brent Laabs (@labster), code review and bug fixes
+
+
+Testing
+-------
+
+Starting from version 4.2.0, LinkTitles finally comes with phpunit tests.
+
+Here's how I set up the testing environment. This may not be the canonical way
+to do it. Basic information on testing MediaWiki can be found [here](https://www.mediawiki.org/wiki/Manual:PHP_unit_testing).
+
+The following assumes that you have an instance of MediaWiki running locally
+on your development machine. This assumes that you are running Linux (I personally
+use Ubuntu).
+
+1. Pull the MediaWiki repository:
+
+        cd ~/Code
+        git clone --depth 1 https://phabricator.wikimedia.org/source/mediawiki.git
+
+2. Install [composer](https://getcomposer.org) locally and fetch the
+  dependencies (including development dependencies):
+
+  Follow the instructions on the [composer download page](https://getcomposer.org/download),
+  but instead of running `php composer-setup.php`, run:
+
+        php composer-setup.php --install-dir=bin --filename=composer
+        bin/composer install
+
+3. Install phpunit (it was already installed on my Ubuntu system when I began
+  testing LinkTitles, so I leave it up to you to figure out how to do it).
+
+4. Copy your `LocalSettings.php` over from your local MediaWiki installation
+  and remove (or comment out) any lines that reference extensions or skins that
+  you are not going to install to your test environment. For the purposes of
+  testing the LinkTitles extension, leave the following line in place:
+
+        wfLoadExtensions( array( 'LinkTitles' ));
+
+  And ensure the settings file contains the following:
+
+        $wgShowDBErrorBacktrace = true;
+
+5. Create a symbolic link to your copy of the LinkTitles repository:
+
+        cd ~/Code/mediawiki/extensions
+        ln -s ~/Code/LinkTitles
+
+6. Make sure your local MediaWiki instance is up to date. Otherwise phpunit may
+  fail and tell you about database problems.
+
+  This is because the local database is used as a template for the unit tests.
+  For example, I initially had MW 1.26 installed on my laptop, but the cloned
+  repository was MW 1.29.1. It's probably also possible to clone the repository
+  with a specific version tag which matches your local installation.
+
+7. Run the tests:
+
+        cd ~/Code/mediawiki/tests/phpunit
+        php phpunit.php --group bovender
+
+  This will run all tests from the 'bovender' group, i.e. tests for my extensions.
+  If you linked just the LinkTitles extension in step 5, only this extension
+  will be tested.