@Test
public void seriesToScreenX_returnsScreenValue() {

    when(xyPlot.getBounds()).thenReturn(new RectRegion(-100, 100, -100, 100));
    assertEquals(0f, graphWidget.seriesToScreenX(-100));
    assertEquals(10f, graphWidget.seriesToScreenX(100));
    assertEquals(5f, graphWidget.seriesToScreenX(0));
}