test: Fix lit and add some tests

Forgot one level of nesting on the lists

Author: dangotbanned

narwhals/_plan/impl_arrow.py

@@ -42,7 +42,8 @@ def lit(node: expr.Literal, frame: NativeFrame) -> Evaluated:  # noqa: ARG001
     import pyarrow as pa
 
     if is_scalar_literal(node.value):
-        return [pa.chunked_array([node.value.unwrap()])]
+        scalar = node.value.unwrap()
+        return [pa.chunked_array([[scalar]])]
     elif is_series_literal(node.value):
         ca = node.value.unwrap().to_native()
         return [t.cast("NativeSeries", ca)]

tests/plan/to_compliant_test.py

@@ -1,11 +1,13 @@
 from __future__ import annotations
 
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Any
 
 import pytest
 
 import narwhals as nw
 import narwhals._plan.demo as nwd
+from narwhals._plan.common import is_expr
+from narwhals._plan.impl_arrow import evaluate as evaluate_pyarrow
 from narwhals.utils import Version
 from tests.namespace_test import backends
 
@@ -14,8 +16,10 @@
     from narwhals._plan.dummy import DummyExpr
 
 
-def _ids_ir(expr: DummyExpr) -> str:
-    return repr(expr._ir)
+def _ids_ir(expr: DummyExpr | Any) -> str:
+    if is_expr(expr):
+        return repr(expr._ir)
+    return repr(expr)
 
 
 @pytest.mark.parametrize(
@@ -35,3 +39,33 @@ def test_to_compliant(backend: BackendName, expr: DummyExpr) -> None:
     namespace = Version.MAIN.namespace.from_backend(backend).compliant
     compliant_expr = expr._to_compliant(namespace)
     assert isinstance(compliant_expr, namespace._expr)
+
+
+@pytest.mark.parametrize(
+    ("expr", "expected"),
+    [
+        (nwd.col("a"), ["A", "B", "A"]),
+        (nwd.col("a", "b"), [["A", "B", "A"], [1, 2, 3]]),
+        (nwd.lit(1), [1]),
+        (nwd.lit(2.0), [2.0]),
+        (nwd.lit(None, nw.String()), [None]),
+    ],
+    ids=_ids_ir,
+)
+def test_evaluate_pyarrow(expr: DummyExpr, expected: Any) -> None:
+    pytest.importorskip("pyarrow")
+    import pyarrow as pa
+
+    data: dict[str, Any] = {
+        "a": ["A", "B", "A"],
+        "b": [1, 2, 3],
+        "c": [9, 2, 4],
+        "d": [8, 7, 8],
+    }
+    frame = pa.table(data)
+    result = evaluate_pyarrow(expr._ir, frame)
+    if len(result) == 1:
+        assert result[0].to_pylist() == expected
+    else:
+        results = [col.to_pylist() for col in result]
+        assert results == expected