implement simple test for downsampling

tests/test_unit/test_transform_utils.py

@@ -0,0 +1,35 @@
+import dask.array as da
+import numpy as np
+import pytest
+from skimage import transform
+
+from brainglobe_template_builder.preproc.transform_utils import (
+    downsample_anisotropic_image_stack,
+)
+
+
+@pytest.fixture()
+def stack():
+    """Create a dask array representing an image stack"""
+    data = np.random.rand(10, 100, 100)  # Random image stack
+    return da.from_array(data, chunks=(1, 100, 100))
+
+
+def test_downsample_anisotropic_image_stack(stack):
+    """Test that downsampling with dask gives same as without."""
+    xy_downsampling = 20
+    z_downsampling = 2
+
+    downsampled_stack = downsample_anisotropic_image_stack(
+        stack, xy_downsampling, z_downsampling
+    )
+
+    assert downsampled_stack.shape == (5, 5, 5)
+
+    expected = transform.downscale_local_mean(
+        stack.compute(), (1, xy_downsampling, xy_downsampling)
+    )
+    expected = transform.downscale_local_mean(expected, (z_downsampling, 1, 1))
+    assert np.all(
+        downsampled_stack == expected
+    ), "dask downsampling does not match expected skimage result"