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.venv/Lib/site-packages/pandas/tests/extension/test_external_block.py

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+import numpy as np
+import pytest
+
+from pandas._libs.internals import BlockPlacement
+import pandas.util._test_decorators as td
+
+import pandas as pd
+from pandas.core.internals import BlockManager
+from pandas.core.internals.blocks import ExtensionBlock
+
+pytestmark = td.skip_array_manager_invalid_test
+
+
+class CustomBlock(ExtensionBlock):
+
+    _holder = np.ndarray
+
+    # Cannot override final attribute "_can_hold_na"
+    @property  # type: ignore[misc]
+    def _can_hold_na(self) -> bool:
+        return False
+
+
+@pytest.fixture
+def df():
+    df1 = pd.DataFrame({"a": [1, 2, 3]})
+    blocks = df1._mgr.blocks
+    values = np.arange(3, dtype="int64")
+    bp = BlockPlacement(slice(1, 2))
+    custom_block = CustomBlock(values, placement=bp, ndim=2)
+    blocks = blocks + (custom_block,)
+    block_manager = BlockManager(blocks, [pd.Index(["a", "b"]), df1.index])
+    return pd.DataFrame(block_manager)
+
+
+def test_concat_axis1(df):
+    # GH17954
+    df2 = pd.DataFrame({"c": [0.1, 0.2, 0.3]})
+    res = pd.concat([df, df2], axis=1)
+    assert isinstance(res._mgr.blocks[1], CustomBlock)