test: Fix more tests to work without polars (and pandas, pyarrow) (#2245)

* test: Fix more tests to work without polars (and pandas, pyarrow)

Split and/or skip tests requiring `polars` when they are unavailable.
Whenever that was a low-hanging fruit, also imports of `pandas`
and `pyarrow` were made optional.

Part of bug #1726

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Fix typing

* Refactor all optional test imports

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Convert duckdb and ibis instances

* Also pa_csv

* Ignore type hints on more tested-invalid calls

* Fix ruff

* Workaround ruff in `ibis_test.py`

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Dan Redding <[email protected]>

Author: 3 people

tests/dependencies/is_into_dataframe_test.py

@@ -28,17 +28,23 @@ def __narwhals_dataframe__(self) -> Self:  # pragma: no cover
 
 
 def test_is_into_dataframe_pyarrow() -> None:
-    pa = pytest.importorskip("pyarrow")
+    pytest.importorskip("pyarrow")
+    import pyarrow as pa
+
     assert is_into_dataframe(pa.table(DATA))
 
 
 def test_is_into_dataframe_polars() -> None:
-    pl = pytest.importorskip("polars")
+    pytest.importorskip("polars")
+    import polars as pl
+
     assert is_into_dataframe(pl.DataFrame(DATA))
 
 
 def test_is_into_dataframe_pandas() -> None:
-    pd = pytest.importorskip("pandas")
+    pytest.importorskip("pandas")
+    import pandas as pd
+
     assert is_into_dataframe(pd.DataFrame(DATA))
     assert is_into_dataframe(nw.from_native(pd.DataFrame(DATA)))
 

tests/dependencies/is_into_series_test.py

@@ -26,17 +26,23 @@ def __narwhals_series__(self) -> Self:  # pragma: no cover
 
 
 def test_is_into_series_pyarrow() -> None:
-    pa = pytest.importorskip("pyarrow")
+    pytest.importorskip("pyarrow")
+    import pyarrow as pa
+
     assert is_into_series(pa.chunked_array([["a", "b"]]))
 
 
 def test_is_into_series_polars() -> None:
-    pl = pytest.importorskip("polars")
+    pytest.importorskip("polars")
+    import polars as pl
+
     assert is_into_series(pl.Series([1, 2, 3]))
 
 
 def test_is_into_series_pandas() -> None:
-    pd = pytest.importorskip("pandas")
+    pytest.importorskip("pandas")
+    import pandas as pd
+
     assert is_into_series(pd.Series([1, 2, 3]))
     assert is_into_series(nw.from_native(pd.Series([1, 2, 3]), series_only=True))
 

tests/dependencies/is_pandas_dataframe_test.py

@@ -11,5 +11,7 @@ def test_is_pandas_dataframe() -> None:
 
 
 def test_not_is_pandas_dataframe() -> None:
-    pl = pytest.importorskip("polars")
+    pytest.importorskip("polars")
+    import polars as pl
+
     assert not is_pandas_dataframe(pl.DataFrame())

tests/dtypes_test.py

@@ -220,8 +220,12 @@ def test_pandas_fixed_offset_1302() -> None:
 
 
 def test_huge_int() -> None:
-    duckdb = pytest.importorskip("duckdb")
-    pl = pytest.importorskip("polars")
+    pytest.importorskip("duckdb")
+    pytest.importorskip("polars")
+
+    import duckdb
+    import polars as pl
+
     df = pl.DataFrame({"a": [1, 2, 3]})
 
     if POLARS_VERSION >= (1, 18):
@@ -251,8 +255,12 @@ def test_huge_int() -> None:
 
 @pytest.mark.skipif(PANDAS_VERSION < (1, 5), reason="too old for pyarrow")
 def test_decimal() -> None:
-    duckdb = pytest.importorskip("duckdb")
-    pl = pytest.importorskip("polars")
+    pytest.importorskip("duckdb")
+    pytest.importorskip("polars")
+
+    import duckdb
+    import polars as pl
+
     df = pl.DataFrame({"a": [1]}, schema={"a": pl.Decimal})
     result = nw.from_native(df).schema
     assert result["a"] == nw.Decimal
@@ -325,8 +333,12 @@ def test_dtype_is_x() -> None:
 
 @pytest.mark.skipif(POLARS_VERSION < (1, 18), reason="too old for Int128")
 def test_huge_int_to_native() -> None:
-    duckdb = pytest.importorskip("duckdb")
-    pl = pytest.importorskip("polars")
+    pytest.importorskip("duckdb")
+    pytest.importorskip("polars")
+
+    import duckdb
+    import polars as pl
+
     df = pl.DataFrame({"a": [1, 2, 3]})
     df_casted = (
         nw.from_native(df).with_columns(a_int=nw.col("a").cast(nw.Int128())).to_native()
@@ -351,8 +363,12 @@ def test_huge_int_to_native() -> None:
 
 
 def test_cast_decimal_to_native() -> None:
-    duckdb = pytest.importorskip("duckdb")
-    pl = pytest.importorskip("polars")
+    pytest.importorskip("duckdb")
+    pytest.importorskip("polars")
+
+    import duckdb
+    import polars as pl
+
     data = {"a": [1, 2, 3]}
 
     df = pl.DataFrame(data)
@@ -372,7 +388,7 @@ def test_cast_decimal_to_native() -> None:
             NotImplementedError, match="Casting to Decimal is not supported yet."
         ):
             (
-                nw.from_native(obj)
+                nw.from_native(obj)  # type: ignore[call-overload]
                 .with_columns(a=nw.col("a").cast(nw.Decimal()))
                 .to_native()
             )

tests/expr_and_series/cast_test.py

@@ -311,12 +311,13 @@ def test_cast_struct(request: pytest.FixtureRequest, constructor: Constructor) -
 
 
 def test_raise_if_polars_dtype(constructor: Constructor) -> None:
-    pl = pytest.importorskip("polars")
+    pytest.importorskip("polars")
+    import polars as pl
 
     for dtype in [pl.String, pl.String()]:
         df = nw.from_native(constructor({"a": [1, 2, 3], "b": [4, 5, 6]}))
         with pytest.raises(TypeError, match="Expected Narwhals dtype, got:"):
-            df.select(nw.col("a").cast(dtype))
+            df.select(nw.col("a").cast(dtype))  # type: ignore[arg-type]
 
 
 def test_cast_time(request: pytest.FixtureRequest, constructor: Constructor) -> None:

tests/expr_and_series/nth_test.py

@@ -39,7 +39,9 @@ def test_nth(
     reason="1.0.0",
 )
 def test_nth_not_supported() -> None:  # pragma: no cover
-    pl = pytest.importorskip("polars")
+    pytest.importorskip("polars")
+    import polars as pl
+
     df = nw.from_native(pl.DataFrame(data))
     with pytest.raises(
         AttributeError, match="`nth` is only supported for Polars>=1.0.0."

tests/frame/arrow_c_stream_test.py

@@ -6,9 +6,13 @@
 from tests.utils import POLARS_VERSION
 from tests.utils import PYARROW_VERSION
 
-pl = pytest.importorskip("polars")
-pa = pytest.importorskip("pyarrow")
-pc = pytest.importorskip("pyarrow.compute")
+pytest.importorskip("polars")
+pytest.importorskip("pyarrow")
+pytest.importorskip("pyarrow.compute")
+
+import polars as pl
+import pyarrow as pa
+import pyarrow.compute as pc
 
 
 @pytest.mark.skipif(POLARS_VERSION < (1, 3), reason="too old for pycapsule in Polars")

tests/frame/getitem_test.py

@@ -45,7 +45,9 @@ def test_slice_rows_with_step(
 
 
 def test_slice_rows_with_step_pyarrow() -> None:
-    pa = pytest.importorskip("pyarrow")
+    pytest.importorskip("pyarrow")
+    import pyarrow as pa
+
     with pytest.raises(
         NotImplementedError,
         match="Slicing with step is not supported on PyArrow tables",
@@ -54,7 +56,9 @@ def test_slice_rows_with_step_pyarrow() -> None:
 
 
 def test_slice_lazy_fails() -> None:
-    pl = pytest.importorskip("polars")
+    pytest.importorskip("polars")
+    import polars as pl
+
     with pytest.raises(TypeError, match="Slicing is not supported on LazyFrame"):
         _ = nw.from_native(pl.LazyFrame(data))[1:]
 

tests/frame/interchange_native_namespace_test.py

@@ -7,7 +7,8 @@
 
 import narwhals.stable.v1 as nw
 
-pl = pytest.importorskip("polars")
+pytest.importorskip("polars")
+import polars as pl
 
 data: Mapping[str, Any] = {"a": [1, 2, 3], "b": [4.5, 6.7, 8.9], "z": ["x", "y", "w"]}
 
@@ -34,7 +35,9 @@ def test_interchange() -> None:
 def test_ibis(
     tmpdir: pytest.TempdirFactory, request: pytest.FixtureRequest
 ) -> None:  # pragma: no cover
-    ibis = pytest.importorskip("ibis")
+    pytest.importorskip("ibis")
+    import ibis
+
     try:
         ibis.set_backend("duckdb")
     except ImportError:
@@ -52,7 +55,9 @@ def test_ibis(
 
 
 def test_duckdb() -> None:
-    duckdb = pytest.importorskip("duckdb")
+    pytest.importorskip("duckdb")
+    import duckdb
+
     df_pl = pl.DataFrame(data)  # noqa: F841
 
     rel = duckdb.sql("select * from df_pl")

tests/frame/interchange_schema_test.py

@@ -9,7 +9,8 @@
 import narwhals.stable.v1 as nw
 from tests.utils import IBIS_VERSION
 
-pl = pytest.importorskip("polars")
+pytest.importorskip("polars")
+import polars as pl
 
 
 def test_interchange_schema() -> None:
@@ -73,7 +74,9 @@ def test_interchange_schema() -> None:
 def test_interchange_schema_ibis(
     tmpdir: pytest.TempdirFactory, request: pytest.FixtureRequest
 ) -> None:  # pragma: no cover
-    ibis = pytest.importorskip("ibis")
+    pytest.importorskip("ibis")
+    import ibis
+
     try:
         ibis.set_backend("duckdb")
     except ImportError:
@@ -164,7 +167,9 @@ def test_interchange_schema_ibis(
 
 
 def test_interchange_schema_duckdb() -> None:
-    duckdb = pytest.importorskip("duckdb")
+    pytest.importorskip("duckdb")
+    import duckdb
+
     df_pl = pl.DataFrame(  # noqa: F841
         {
             "a": [1, 1, 2],