TST: Add tests for faulty behavior relating to pyarrow categoricals

Author: robin-mader-bis

pandas/tests/reshape/test_pivot.py

@@ -3,6 +3,7 @@
     datetime,
     timedelta,
 )
+import io
 from itertools import product
 import re
 
@@ -2851,3 +2852,42 @@ def test_pivot_margins_with_none_index(self):
             ),
         )
         tm.assert_frame_equal(result, expected)
+
+    def test_pivot_with_pyarrow_categorical(self):
+        # GH#53051
+
+        # Create dataframe with categorical colum
+        df = (
+            pd.DataFrame([("A", 1), ("B", 2), ("C", 3)], columns=["string_column", "number_column"])
+            .astype({"string_column": "string", "number_column": "float32"})
+            .astype({"string_column": "category", "number_column": "float32"})
+        )
+
+        # Convert dataframe to pyarrow backend
+        with io.BytesIO() as buffer:
+            df.to_parquet(buffer)
+            buffer.seek(0)  # Reset buffer position
+            df = pd.read_parquet(buffer, dtype_backend="pyarrow")
+
+
+        # Check that pivot works
+        df = df.pivot(columns=["string_column"], values=["number_column"])
+
+        # Assert that values of result are correct to prevent silent failure
+        multi_index = pd.MultiIndex.from_arrays(
+            [
+                ["number_column", "number_column", "number_column"],
+                ["A", "B", "C"]
+            ],
+            names=(None, "string_column")
+        )
+        df_expected = pd.DataFrame(
+            [
+                [1.0, np.nan, np.nan],
+                [np.nan, 2.0, np.nan],
+                [np.nan, np.nan, 3.0]
+            ],
+            columns=multi_index
+        )
+        tm.assert_frame_equal(df, df_expected, check_dtype=False, check_column_type=False)
+

pandas/tests/test_multilevel.py

@@ -1,4 +1,5 @@
 import datetime
+import io
 
 import numpy as np
 import pytest
@@ -318,6 +319,26 @@ def test_multiindex_dt_with_nan(self):
         expected = Series(["a", "b", "c", "d"], name=("sub", np.nan))
         tm.assert_series_equal(result, expected)
 
+    def test_multiindex_with_pyarrow_categorical(self):
+        # GH#53051
+
+        # Create dataframe with categorical colum
+        df = (
+            pd.DataFrame([("A", 1), ("B", 2), ("C", 3)], columns=["string_column", "number_column"])
+            .astype({"string_column": "string", "number_column": "float32"})
+            .astype({"string_column": "category", "number_column": "float32"})
+        )
+
+        # Convert dataframe to pyarrow backend
+        with io.BytesIO() as buffer:
+            df.to_parquet(buffer)
+            buffer.seek(0)  # Reset buffer position
+            df = pd.read_parquet(buffer, dtype_backend="pyarrow")
+
+
+        # Check that index can be set
+        df.set_index(["string_column", "number_column"])
+
 
 class TestSorted:
     """everything you wanted to test about sorting"""