Create README.troubleshooting.md

tests/README.troubleshooting.md

+# Troubleshooting Piwik Tests
+
+If you have problems with running Piwik tests see below. 
+
+If you cannot solve your issues please [ask in the forums](http://forum.piwik.org/list.php?9)
+
+## Using latest GIT version
+On ubuntu to use the latest GIT:
+
+```
+sudo add-apt-repository ppa:git-core/ppa
+sudo apt-get update
+sudo apt-get upgrade
+```
+
+## PHP 5.5: also update PHPUnit to latest
+
+See [PHPUnit update](http://phpunit.de/manual/current/en/installation.html) or try this command:
+
+    $ sudo pear install -a phpunit/PHPUnit
+
+## Troubleshooting failing tests
+
+If you get any of these errors:
+ * `RuntimeException: Unable to create the cache directory ( piwik/tmp/templates_c/66/77).`
+ * or `fopen( piwik/tmp/latest/testgz.txt): failed to open stream: No such file or directory`
+ * or `Exception: Error while creating the file: piwik/tmp/latest/LATEST`
+ * or `PHP Warning:  file_put_contents( piwik/tmp/logs/piwik.test.log): failed to open stream: Permission denied in [..]`
+
+On your dev server, give your user permissions to write to the directory:
+
+    $ sudo chmod 777 -R piwik/tmp/
+
+## Troubleshooting SLOW tests
+
+If the tests are running incredibly slow on your machine, maybe you are running mysql DB on an ext4 partition?
+Here is the tip that will save you hours of research: if you use Mysql on ext4 partition,
+make sure you add "nobarrier" option to /etc/fstab to disable some super slow IO feature.
+
+Change from:
+    `UUID=83237e54-445f-8b83-180f06459d46       /       ext4    errors=remount-ro     0       1`
+to this:
+    `UUID=83237e54-445f-8b83-180f06459d46       /       ext4    errors=remount-ro,nobarrier     0       1`
+