Initial public release

backend/tests/test_raster_cell_selection.py

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+"""A selection smaller than a raster cell must not silently read as zero.
+
+``geometry_mask`` selects a cell when its *centre* falls inside the geometry.
+A rectangle smaller than one cell, or one that lands between four centres,
+therefore selects nothing at all — and the analysis returned zeros, which on
+screen is indistinguishable from "we looked and there is nothing here". On a
+100 m population raster a 40 m rectangle over a city block reported no
+inhabitants.
+
+Selection now falls back to every touched cell and says that it did, so the
+value is readable as "at least one whole cell", not as an empty area.
+"""
+
+from __future__ import annotations
+
+import pytest
+
+np = pytest.importorskip("numpy")
+rasterio = pytest.importorskip("rasterio")
+
+from rasterio.transform import from_origin  # noqa: E402 - optional rasterio gate precedes imports
+from shapely.geometry import box  # noqa: E402 - optional rasterio gate precedes imports
+
+from app.services.raster_cell_selection import select_cells  # noqa: E402 - optional rasterio gate precedes service import
+
+
+# 100 m cells, origin at the top-left corner of a 3x3 grid.
+TRANSFORM = from_origin(200_000, 210_000, 100.0, 100.0)
+SHAPE = (3, 3)
+
+
+def test_a_normal_selection_uses_cell_centres() -> None:
+    selection = select_cells(box(200_000, 209_700, 200_300, 210_000), out_shape=SHAPE, transform=TRANSFORM)
+
+    assert selection.mask.sum() == 9
+    assert selection.mode == "cell_centre"
+    assert selection.expanded_to_touched_cells is False
+    assert selection.warning is None
+
+
+def test_a_rectangle_smaller_than_one_cell_still_returns_that_cell() -> None:
+    selection = select_cells(box(200_010, 209_960, 200_050, 209_990), out_shape=SHAPE, transform=TRANSFORM)
+
+    assert selection.mask.sum() == 1
+    assert selection.mode == "all_touched"
+    assert selection.expanded_to_touched_cells is True
+    assert "cel" in selection.warning
+
+
+def test_a_rectangle_between_four_cell_centres_returns_all_four() -> None:
+    selection = select_cells(box(200_080, 209_880, 200_120, 209_920), out_shape=SHAPE, transform=TRANSFORM)
+
+    assert selection.mask.sum() == 4
+    assert selection.expanded_to_touched_cells is True
+
+
+def test_a_selection_entirely_off_the_raster_selects_nothing() -> None:
+    """Falling back must not invent coverage where the geometry does not reach."""
+
+    selection = select_cells(box(300_000, 300_000, 300_100, 300_100), out_shape=SHAPE, transform=TRANSFORM)
+
+    assert selection.mask.sum() == 0
+    assert selection.expanded_to_touched_cells is False
+    assert selection.mode == "cell_centre"
+
+
+def test_the_warning_states_how_much_larger_the_analysed_area_is() -> None:
+    selection = select_cells(
+        box(200_010, 209_960, 200_050, 209_990),
+        out_shape=SHAPE,
+        transform=TRANSFORM,
+        cell_area_m2=100.0 * 100.0,
+    )
+
+    # One 100x100 m cell was analysed for a 40x30 m request.
+    assert "1 rastercel" in selection.warning
+    assert "1.0 ha" in selection.warning
+
+
+def test_the_mask_shape_always_matches_the_raster_window() -> None:
+    selection = select_cells(box(200_010, 209_960, 200_050, 209_990), out_shape=SHAPE, transform=TRANSFORM)
+
+    assert selection.mask.shape == SHAPE
+    assert selection.mask.dtype == np.bool_