Add tests for dtype_to_arrow_c_fmt

Signed-off-by: Vasily Litvinov <[email protected]>

Author: vnlitvinov

pandas/core/exchange/utils.py

@@ -2,15 +2,13 @@
 Utility functions and objects for implementing the exchange API.
 """
 
-import enum
 import pandas as pd
 import re
 import numpy as np
 from pandas.api.types import is_datetime64_dtype
 
 
-@enum.unique
-class ArrowCTypes(enum.Enum):
+class ArrowCTypes:
     """
     Enum for Apache Arrow C type format strings.
 

pandas/tests/exchange/test_utils.py

@@ -0,0 +1,35 @@
+import pandas as pd
+import numpy as np
+import pytest
+
+from pandas.core.exchange.utils import dtype_to_arrow_c_fmt
+
+# TODO: use ArrowSchema to get reference C-string.
+# At the time, there is no way to access ArrowSchema holding a type format string from python.
+# The only way to 'touch' it is to export the structure to a C-pointer:
+# https://github.com/apache/arrow/blob/5680d209fd870f99134e2d7299b47acd90fabb8e/python/pyarrow/types.pxi#L230-L239
+@pytest.mark.parametrize(
+    "pandas_dtype, c_string",
+    [
+        (np.dtype("bool"), "b"),
+        (np.dtype("int8"), "c"),
+        (np.dtype("uint8"), "C"),
+        (np.dtype("int16"), "s"),
+        (np.dtype("uint16"), "S"),
+        (np.dtype("int32"), "i"),
+        (np.dtype("uint32"), "I"),
+        (np.dtype("int64"), "l"),
+        (np.dtype("uint64"), "L"),
+        (np.dtype("float16"), "e"),
+        (np.dtype("float32"), "f"),
+        (np.dtype("float64"), "g"),
+        (pd.Series(["a"]).dtype, "u"),
+        (
+            pd.Series([0]).astype("datetime64[ns]").dtype,
+            "tsn:",
+        ),
+    ],
+)
+def test_dtype_to_arrow_c_fmt(pandas_dtype, c_string):  # noqa PR01
+    """Test ``dtype_to_arrow_c_fmt`` utility function."""
+    assert dtype_to_arrow_c_fmt(pandas_dtype) == c_string