<extension point="org.eclipse.ui.menus">
    <menuContribution locationURI="popup:MyNavigatorView.popupMenu">
        <command commandId="my.command.id" label="my command label"
            style="push" >
        <visibleWhen>
                <with variable="activeMenuSelection">
                    <iterate ifEmpty="false">
                        <adapt type="org.eclipse.core.resources.IFolder">
<!--                            <test property="org.eclipse.core.resources.name" value="MyDirectory" />   -->  <!-- such property tester works ! -->
                                <test property="my.plugin.dirtype" value="MyDirectory" />
                        </adapt>
                    </iterate>
                </with>                 
            </visibleWhen>
        </command>
    </menuContribution>
</extension>

<extension point="org.eclipse.ui.commands">
    <command description="Do something with a model element" id="my.command.id"
        name="Do Something">
    </command>
</extension>

<extension point="org.eclipse.ui.handlers">
    <handler
        class="my.plugin.AddFormHandler"
        commandId="my.command.id">

    </handler>
</extension>

<extension point="org.eclipse.core.expressions.propertyTesters">
    <propertyTester
        class="my.plugin.DirTypePropertyTester"
        id="my.plugin.dirTypePropertyTester"
        namespace="my.plugin"
        properties="dirtype"
        type="org.eclipse.core.resources.IResource">
    </propertyTester>
</extension>