fix: support converting empty time Series to pyarrow Array

Author: tswast

tests/unit/test_arrow.py

@@ -0,0 +1,70 @@
+# Copyright 2021 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import datetime as dt
+
+import pandas
+import pyarrow
+import pytest
+
+# To register the types.
+import db_dtypes  # noqa
+
+
+@pytest.mark.parametrize(
+    ("series", "expected"),
+    (
+        (pandas.Series([], dtype="date"), pyarrow.array([], type=pyarrow.date32())),
+        (
+            pandas.Series([None, None, None], dtype="date"),
+            pyarrow.array([None, None, None], type=pyarrow.date32()),
+        ),
+        (
+            pandas.Series(
+                [dt.date(2021, 9, 27), None, dt.date(2011, 9, 27)], dtype="date"
+            ),
+            pyarrow.array(
+                [dt.date(2021, 9, 27), None, dt.date(2011, 9, 27)],
+                type=pyarrow.date32(),
+            ),
+        ),
+        (
+            pandas.Series(
+                [dt.date(1677, 9, 22), dt.date(1970, 1, 1), dt.date(2262, 4, 11)],
+                dtype="date",
+            ),
+            pyarrow.array(
+                [dt.date(1677, 9, 22), dt.date(1970, 1, 1), dt.date(2262, 4, 11)],
+                type=pyarrow.date32(),
+            ),
+        ),
+        (pandas.Series([], dtype="time"), pyarrow.array([], type=pyarrow.time64("ns"))),
+        (
+            pandas.Series([None, None, None], dtype="time"),
+            pyarrow.array([None, None, None], type=pyarrow.time64("ns")),
+        ),
+        (
+            pandas.Series(
+                [dt.time(0, 0, 0, 0), None, dt.time(23, 59, 59, 999_999)], dtype="time"
+            ),
+            pyarrow.array(
+                [dt.time(0, 0, 0, 0), None, dt.time(23, 59, 59, 999_999)],
+                type=pyarrow.time64("ns"),
+            ),
+        ),
+    ),
+)
+def test_to_arrow(series, expected):
+    array = pyarrow.array(series)
+    assert array.equals(expected)