Added failing unit tests

[nabobalis]

No description provided.

[DanRyanIrish]

Hi @nabobalis. It looks to me that the time world axis is also coupled to the celestial world axes via a common pixel axis. So in order to unambiguously determine a point in the cube associated with a time, you also have to provide a SkyCoord, which you haven't done. That's why the error message is saying that it expects 2 inputs ((SkyCoord, Time)) when you have only given it one (Time).

I'm not sure that there is a general solution that gets around this problem with this WCS. Alternatively, you could use the cube.extra_coords.cube_wcs instead of combined_wcs. Since this adds dummy world axes in units of pixels for pixel/array axes not associated with any extra coords, its output of

tuple(val[0] for val in cube.extra_coords.cube_wcs.world_axis_object_classes.values())

is

(Time, Quantity, Quantity)

In that case, I think your corners would become:

    lower_corner = (Time("2000-01-01T15:00:00", scale="utc", format="fits"), None, None)
    upper_corner = (Time("2000-01-01T20:00:00", scale="utc", format="fits"), None, None)

[nabobalis]

With that change, I get:
test_crop_by_extra_coords_using_combined_wcs - ValueError: 3 components in point 0 do not match WCS with 4 components.

If I add another None,

TypeError: <class 'astropy.time.core.Time'> of component 0 in point 0 is incompatible with WCS component spectral_0 <class 'astropy.units.quantity.Quantity'>.

In that block, the order seems to be ['spectral_0', 'celestial_0', 'temporal_1', 'PIXEL_1']