Adding icon to the plugin

Acoarding to the Intellij confluence page regarding icons and images http://confluence.jetbrains.com/display/IDEADEV/Work+with+Icons+and+Images

I should be able to do add a icon like so:

<action id="TestListSynchronizer.Menu"
             icon="/icons/testSynchronizer.png"
             description="Synchronize your tests to the database">
          <add-to-group group-id="MainToolBar" anchor="last"/>
          <keyboard-shortcut keymap="$default" first-keystroke="shift ctrl S"/>
</action>

but I get a error message "Icon cannot be found in '/icons/testSynchronizer.png'", you can see on the image the exact structure of the project and the error message.