TST: 31739 - add coverage of subtracting datetimes w/differing timezones

Author: AnjoMan

pandas/conftest.py

@@ -1080,26 +1080,30 @@ def iris(datapath):
 # ----------------------------------------------------------------
 # Time zones
 # ----------------------------------------------------------------
-TIMEZONES = [
-    None,
-    "UTC",
-    "US/Eastern",
-    "Asia/Tokyo",
-    "dateutil/US/Pacific",
-    "dateutil/Asia/Singapore",
-    "+01:15",
-    "-02:15",
-    "UTC+01:15",
-    "UTC-02:15",
-    tzutc(),
-    tzlocal(),
-    FixedOffset(300),
-    FixedOffset(0),
-    FixedOffset(-300),
-    timezone.utc,
-    timezone(timedelta(hours=1)),
-    timezone(timedelta(hours=-1), name="foo"),
+
+# contains a list of different timezones in a number of formats, along with the
+# matched offset from UTC
+TIMEZONE_MAPPING = [
+    (None, None),
+    ("UTC", Timedelta("0 days")),
+    ("US/Eastern", Timedelta("-5 hours")),
+    ("Asia/Tokyo", Timedelta("9 hours")),
+    ("dateutil/US/Pacific", Timedelta("-8 hours")),
+    ("dateutil/Asia/Singapore", Timedelta("8 hours")),
+    ("+01:15", Timedelta("1 hour 15 minutes")),
+    ("-02:15", Timedelta("-2 hours 15 minutes")),
+    ("UTC+01:15", Timedelta("1 hour 15 minutes")),
+    ("UTC-02:15", Timedelta("-2 hours 15 minutes")),
+    (tzutc(), Timedelta("0 seconds")),
+    (tzlocal(), None),
+    (FixedOffset(300), Timedelta("300 minutes")),
+    (FixedOffset(0), Timedelta("0 minutes")),
+    (FixedOffset(-300), Timedelta("-300 minutes")),
+    (timezone.utc, Timedelta("0 seconds")),
+    (timezone(timedelta(hours=1)), Timedelta("1 hours")),
+    (timezone(timedelta(hours=-1), name="foo"), Timedelta("-1 hours")),
 ]
+TIMEZONES = [i for (i, _) in TIMEZONE_MAPPING]
 TIMEZONE_IDS = [repr(i) for i in TIMEZONES]
 
 
@@ -1121,6 +1125,15 @@ def tz_aware_fixture(request):
     return request.param
 
 
+@pytest.fixture
+def tz_aware_utc_offset_fixture(tz_aware_fixture):
+    """
+    Expected tz offset from UTC for each key in TIMEZONE_MAPPING
+    """
+    tz, expected_offset = TIMEZONE_MAPPING[TIMEZONES.index(tz_aware_fixture)]
+    return expected_offset
+
+
 # Generate cartesian product of tz_aware_fixture:
 tz_aware_fixture2 = tz_aware_fixture
 

pandas/tests/scalar/timestamp/test_arithmetic.py

@@ -4,6 +4,7 @@
     timezone,
 )
 
+from dateutil.tz import tzlocal
 import numpy as np
 import pytest
 
@@ -141,6 +142,21 @@ def test_subtracting_involving_datetime_with_different_tz(self):
         assert isinstance(result, Timedelta)
         assert result == Timedelta("-1 days +18:00:00")
 
+    def test_subtracting_different_timezones(
+        self, tz_aware_fixture, tz_aware_utc_offset_fixture
+    ):
+        if tz_aware_fixture == tzlocal():
+            pytest.skip("Subtraction won't work for naive tz")
+
+        t_raw = Timestamp("20130101")
+        t_UTC = t_raw.tz_localize("UTC")
+        t_diff = t_raw.tz_localize(tz_aware_fixture)
+
+        result = t_UTC - t_diff
+
+        assert isinstance(result, Timedelta)
+        assert result == tz_aware_utc_offset_fixture
+
     def test_addition_subtraction_types(self):
         # Assert on the types resulting from Timestamp +/- various date/time
         # objects