testValueFromMousePosition() {
    const value = 30;
    oneThumbSlider.setValue(value);
    /** @suppress {visibility} suppression added to enable type checking */
    const offset = style.getPageOffset(oneThumbSlider.valueThumb);
    /** @suppress {visibility} suppression added to enable type checking */
    const size = style.getSize(oneThumbSlider.valueThumb);
    offset.x += size.width / 2;
    offset.y += size.height / 2;
    let e = null;
    events.listen(oneThumbSlider, EventType.MOUSEMOVE, (evt) => {
      e = evt;
    });
    testingEvents.fireMouseMoveEvent(oneThumbSlider, offset);
    assertNotEquals(e, null);
    assertRoughlyEquals(
        value, Math.round(oneThumbSlider.getValueFromMousePosition(e)), 1);
    // Verify this works regardless of current position.
    oneThumbSlider.setValue(value / 2);
    assertRoughlyEquals(
        value, Math.round(oneThumbSlider.getValueFromMousePosition(e)), 1);
  }
Tests getValueFromMousePosition method.
@suppress {checkTypes} suppression added to enable type checking