Add basic tests of dataframe scan

Also assert that unsupported file scan operations raise.

python/cudf_polars/tests/test_dataframescan.py

@@ -0,0 +1,43 @@
+# SPDX-FileCopyrightText: Copyright (c) 2024 NVIDIA CORPORATION & AFFILIATES.
+# SPDX-License-Identifier: Apache-2.0
+
+from __future__ import annotations
+
+import pytest
+
+import polars as pl
+
+from cudf_polars.testing.asserts import assert_gpu_result_equal
+
+
+@pytest.mark.parametrize(
+    "subset",
+    [
+        None,
+        ["a", "c"],
+        ["b", "c", "d"],
+        ["b", "d"],
+        ["b", "c"],
+        ["c", "e"],
+        ["d", "e"],
+        pl.selectors.string(),
+        pl.selectors.integer(),
+    ],
+)
+@pytest.mark.parametrize("predicate_pushdown", [False, True])
+def test_scan_drop_nulls(subset, predicate_pushdown):
+    df = pl.LazyFrame(
+        {
+            "a": [1, 2, 3, 4],
+            "b": [None, 4, 5, None],
+            "c": [6, 7, None, None],
+            "d": [8, None, 9, 10],
+            "e": [None, None, "A", None],
+        }
+    )
+    # Drop nulls are pushed into filters
+    q = df.drop_nulls(subset)
+
+    assert_gpu_result_equal(
+        q, collect_kwargs={"predicate_pushdown": predicate_pushdown}
+    )

python/cudf_polars/tests/test_scan.py

@@ -6,6 +6,7 @@
 
 import polars as pl
 
+from cudf_polars import translate_ir
 from cudf_polars.testing.asserts import assert_gpu_result_equal
 
 
@@ -86,3 +87,12 @@ def test_scan(df, columns, mask):
     if columns is not None:
         q = df.select(*columns)
     assert_gpu_result_equal(q)
+
+
+def test_scan_unsupported_raises(tmp_path):
+    df = pl.DataFrame({"a": [1, 2, 3]})
+
+    df.write_ndjson(tmp_path / "df.json")
+    q = pl.scan_ndjson(tmp_path / "df.json")
+    with pytest.raises(NotImplementedError):
+        _ = translate_ir(q._ldf.visit())