def METHOD_NAME(self):
    """Test that columns with date values have UTC time scale"""
    df = pd.DataFrame(
        {"index": [date(2019, 8, 9), date(2019, 8, 10)], "numbers": [1, 10]}
    ).set_index("index")
    chart, _ = altair.generate_chart("line", df)
    st._legacy_altair_chart(chart)
    c = self.get_delta_from_queue().new_element.vega_lite_chart
    spec_dict = json.loads(c.spec)
    # The x axis should have scale="utc", because it uses date values.
    x_scale = _deep_get(spec_dict, "encoding", "x", "scale", "type")
    self.assertEqual(x_scale, "utc")
    # The y axis should _not_ have scale="utc", because it doesn't
    # use date values.
    y_scale = _deep_get(spec_dict, "encoding", "y", "scale", "type")
    self.assertNotEqual(y_scale, "utc")