diff --git a/tests/test_georaster.py b/tests/test_georaster.py
index 3648400..1287efe 100644
--- a/tests/test_georaster.py
+++ b/tests/test_georaster.py
@@ -910,6 +910,7 @@ def rasters_for_testing_chunks():
 
 def test_join_use_mask_band():
     # https://github.com/OSGeo/gdal/issues/1148
+    # The test checks the pixel at the coordinate of bottom left corner of the r2 raster is unmasked.
     r1 = GeoRaster2.open("tests/data/raster/overlap1.tif")
     r2 = GeoRaster2.open("tests/data/raster/overlap2.tif")
     joined = join([r1, r2])