fix: use datetime timezone info when generating timestamp strings (#236)

* fix: use datetime timezone when generating timestamp strings

* style: fix lint

Co-authored-by: larkee <larkee@users.noreply.github.com>

google/cloud/spanner_v1/_helpers.py

@@ -118,7 +118,7 @@ def _make_value_pb(value):
     if isinstance(value, datetime_helpers.DatetimeWithNanoseconds):
         return Value(string_value=value.rfc3339())
     if isinstance(value, datetime.datetime):
-        return Value(string_value=_datetime_to_rfc3339(value))
+        return Value(string_value=_datetime_to_rfc3339(value, ignore_zone=False))
     if isinstance(value, datetime.date):
         return Value(string_value=value.isoformat())
     if isinstance(value, six.binary_type):

tests/unit/test__helpers.py

@@ -215,6 +215,18 @@ def test_w_datetime(self):
         self.assertIsInstance(value_pb, Value)
         self.assertEqual(value_pb.string_value, datetime_helpers.to_rfc3339(now))
 
+    def test_w_timestamp_w_tz(self):
+        import datetime
+        import pytz
+        from google.protobuf.struct_pb2 import Value
+
+        when = datetime.datetime(
+            2021, 2, 8, 0, 0, 0, tzinfo=pytz.timezone("US/Mountain")
+        )
+        value_pb = self._callFUT(when)
+        self.assertIsInstance(value_pb, Value)
+        self.assertEqual(value_pb.string_value, "2021-02-08T07:00:00.000000Z")
+
     def test_w_numeric(self):
         import decimal
         from google.protobuf.struct_pb2 import Value