'Text in combos is wiped away when there is no data and mosaic disappears as well.
GH-2459
GH-2462'

def test_combos_and_mosaic(self):

    def assertCount(cb_color, cb_attr, areas):
        self.assertEqual(len(self.widget.areas), areas)
        self.assertEqual(self.widget.cb_attr_color.count(), cb_color)
        for (i, combo) in enumerate(self.widget.attr_combos):
            self.assertEqual(combo.count(), cb_attr[i])
    data = Table('iris')
    assertCount(1, [0, 0, 0, 0], 0)
    self.send_signal(self.widget.Inputs.data, data)
    assertCount(6, [5, 6, 6, 6], 16)
    self.send_signal(self.widget.Inputs.data, None)
    assertCount(1, [0, 0, 0, 0], 0)
