### Question:
FxUiManager { public void startGui(final Stage mainStage) { try { onStageCreated(mainStage); final Scene mainScene = getScene(mainComponent()); onSceneCreated(mainScene); mainStage.setScene(mainScene); mainStage.setTitle(title()); Option.ofOptional(getStylesheet()) .filter(style -> !FxmlStylesheets.DEFAULT_JAVAFX_STYLE.equals(style)) .peek(stylesheet -> this.setTheme(stylesheet, mainStage)); mainStage.show(); } catch (Throwable t) { throw new RuntimeException("There was a failure during start-up of the application.", t); } }  void startGui(final Stage mainStage); @Autowired void setEasyFxml(EasyFxml easyFxml);  }### Answer:
@Test public void startGui() { Platform.runLater(() -> testFxUiManager.startGui(stage)); }