@Test
  void showDrawerInputValidation() {
    robot.interact(() -> {
      // null check
      assertThrows(NullPointerException.class, () -> workbench.showDrawer(drawer, null, 0));
      assertThrows(NullPointerException.class, () -> workbench.showDrawer(null, Side.LEFT, 0));

      // Percentage range
      assertThrows(IllegalArgumentException.class,
          () -> workbench.showDrawer(drawer, Side.LEFT, Integer.MIN_VALUE));
      assertThrows(IllegalArgumentException.class,
          () -> workbench.showDrawer(drawer, Side.LEFT, -2));
      workbench.showDrawer(drawer, Side.LEFT, -1); // valid
      workbench.showDrawer(drawer, Side.LEFT, 0); // valid
      workbench.showDrawer(drawer, Side.LEFT, 1); // valid
      workbench.showDrawer(drawer, Side.LEFT, 100); // valid
      assertThrows(IllegalArgumentException.class,
          () -> workbench.showDrawer(drawer, Side.LEFT, 101));
      assertThrows(IllegalArgumentException.class,
          () -> workbench.showDrawer(drawer, Side.LEFT, Integer.MAX_VALUE));
    });
  }
Internal testing method which returns the currently shown overlay.
workbenchfx-core/src/test/java/com/dlsc/workbenchfx/WorkbenchTest.java