@Test
public void seriesToScreenY_returnsScreenValue() {

    when(xyPlot.getBounds()).thenReturn(new RectRegion(-100, 100, -100, 100));
    assertEquals(100f, graphWidget.seriesToScreenY(100));
    assertEquals(0f, graphWidget.seriesToScreenY(-100));
    assertEquals(50f, graphWidget.seriesToScreenY(0));
}