GWT module name for client component test

I'm trying to write a test for client-side GWT component. My gwt.xml file is placed in subproject-name/src/main/resources/editor.gwt.xml. I expect my module to be named main.resources.editor. I wrote a test:

public class PlacementPageTest extends GWTTestCase {

    PlacementPage testee = new PlacementPage();

    @Test
    public void test() {
        testee.activate();
    }

    @Override
    public String getModuleName() {
        return "main.resources.editor";
    }
}

I'm getting error stating: ERROR: GWT.create() is only usable in client code!...

Other answers I found suggest that I supplied a wrong module name. How do I find the right module name?