I can't seem to hit the following lines -

@ntessore do you have a specific case in mind that'll hit these lines. Every combination of arguments I have tried results in q[-1] == count, size is always 0, and putting these values in, it does not matter what batch is, the condition is never met.

@ntessore do you have a specific case in mind that'll hit these lines. Every combination of arguments I have tried results in q[-1] == count, size is always 0, and putting these values in, it does not matter what batch is, the condition is never met.

Ah, good catch. The reason is that the batching processes 1000 pixels at a time, but we are using HEALPix maps with only 12 pixels as inputs.

Solution: use a higher number of pixels (npix) and replace all uses of 12 with npix, and add another case where some of the visibility is zero (hence it needs many batches of empty pixels until it finds enough points).

def test_positions_from_delta():  # type: ignore[no-untyped-def]

    # create maps that saturate the batching in the function
    nside = 128
    npix = 12 * nside**2

    # case: single-dimensional input

    ngal = 1e-3
    delta = np.zeros(npix)
    bias = 0.8
    vis = np.ones(npix)

    ...

    # case: only the southern hemisphere is visible

    vis[:vis.size//2] = 0.0

    lon, lat, cnt = catpos(positions_from_delta(ngal, delta, bias, vis))  # type: ignore[no-untyped-call]

    assert cnt.shape == (3, 2)
    assert lon.shape == (cnt.sum(),)
    assert lat.shape == (cnt.sum(),)

I see, thanks for the detailed suggestion, @ntessore! I will apply this to the tests.