title: TestFX cannot localize node during Travis CI build after tested application was opened another window
body: <p>I am working on simple java standalone application with GUI created with JavaFX 8. </p>
  
  <p>I wrote some tests of GUI with TestFX framework (version 3.1.0). On my local machine tests works fine, but they are failed on Travis CI environment. Please take a look, some fragments of code:</p>
  
  <pre><code>import static org.assertj.core.api.Assertions.assertThat;
  import static org.loadui.testfx.GuiTest.find;
  
  public class JavafxApplicationIT {
      private static GuiTest controller;
  
      @BeforeClass
      public static void setAfter() throws Exception {
          FXTestUtils.launchApp(JavafxApplication.class);
          Thread.sleep(5000);
          controller = new GuiTest() {
              @Override
              protected Parent getRootNode() {
                  return JavafxApplication.getScene().getRoot();
              }
          };
      }
  
      @AfterClass
      public static void shutdownAll() throws InterruptedException {
          Platform.runLater(() -&gt; JavafxApplication.getStage().close());
      }
  
      @Test
      public void shouldFillForm_saveLicence_thenOpen_andVerifySignature() throws Throwable {
          controller.click("#newLicenceButton");
  
          ((TextField) find("#licenceUidField")).setText(licenceUID);
          ((TextField) find("#customerIdField")).setText(customerId);
          ....
          controller.click("#mainActionButton");
          Thread.sleep(3000);
          ((TextField) find("#licFileField")).setText(licenceFile.getPath()); // &lt;--- FAILED
  
      }
  }
  </code></pre>
  
  <p>I've got <code>No nodes matched '#licFileField'</code> error. I notice that in every failing cases problem with matching is always after opening some new window in application. </p>
  
  <p>In above case, clicking on <code>mainActionButton</code> invokes new window, and <code>licFileField</code> is a name of element from new (active) window.</p>
  
  <p>Maybe it is connected with configuration of xvfb on Travis CI machine? In <code>.travis.yml</code> I've got:</p>
  
  <pre><code>before_install:
    - "export DISPLAY=:99.0"
    - "sh -e /etc/init.d/xvfb start"
    - "/sbin/start-stop-daemon --start --quiet --pidfile /tmp/custom_xvfb_99.pid --make-pidfile --background --exec /usr/bin/Xvfb -- :99 -ac -screen 0 1280x1024x16"
  </code></pre>