accel: add tests for failure branches in scatter/argsort

Author: mdekstrand

src/lenskit/_accel/data.pyi

@@ -37,8 +37,16 @@ def dense_cooc(
     *,
     diagonal: bool = True,
 ) -> AccelTask[np.ndarray[tuple[int, int], np.dtype[np.float32]]]: ...
-def scatter_array(dst: _A, idx: pa.Array, src: _A) -> _A: ...
-def scatter_array_empty(dst_size: int, idx: pa.Array, src: _A) -> _A: ...
+def scatter_array(dst: _A, idx: pa.Array, src: _A) -> _A:
+    """
+    Create a new array merging a base array with the scattered content of a second array.
+    """
+
+def scatter_array_empty(dst_size: int, idx: pa.Array, src: _A) -> _A:
+    """
+    Scatter array elements into a new, otherwise-empty array.
+    """
+
 def sample_negatives(
     coords: CoordinateTable,
     rows: np.ndarray[tuple[int], np.dtype[np.int32]],

tests/accel/test_argsort.py

@@ -10,7 +10,7 @@
 import hypothesis.extra.numpy as nph
 import hypothesis.strategies as st
 from hypothesis import given
-from pytest import mark
+from pytest import mark, raises
 
 from lenskit._accel import data
 
@@ -209,3 +209,9 @@ def test_topn_any_float(arr, n):
         mask[np.isnan(arr)] = False
         nopes = arr[mask]
         assert np.all(nopes <= np.min(items))
+
+
+def test_topn_rejects_strings():
+    strings = pa.array(["a", "b", "c", "x", "9", "0", "3", "@"])
+    with raises(TypeError):
+        data.argtopn(strings, 5)

tests/accel/test_scatter.py

@@ -12,6 +12,7 @@
 import hypothesis.extra.numpy as nph
 import hypothesis.strategies as st
 from hypothesis import given
+from pytest import raises
 
 from lenskit._accel import data
 
@@ -82,3 +83,15 @@ def test_scatter_dst_size(hd: st.DataObject, size, idx_t: np.dtype):
     arr = arr_a.to_numpy(zero_copy_only=False)
 
     assert np.array_equal(arr[idx], src, equal_nan=True)
+
+
+def test_scatter_rejects_strings():
+    strings = pa.array(["a", "b", "c", "x", "9", "0", "3", "@"])
+    with raises(TypeError):
+        data.scatter_array(strings, pa.array([2, 7, 0]), strings)
+
+
+def test_scatter_empty_rejects_strings():
+    strings = pa.array(["a", "b", "c", "x", "9", "0", "3", "@"])
+    with raises(TypeError):
+        data.scatter_array_empty(100, pa.array([2, 7, 0]), strings)