TST: lock down timeseries now tests, xref #18666

pandas/_libs/tslib.pyx

@@ -211,7 +211,7 @@ def _test_parse_iso8601(object ts):
     if ts == 'now':
         return Timestamp.utcnow()
     elif ts == 'today':
-        return Timestamp.utcnow().normalize()
+        return Timestamp.now().normalize()
 
     _string_to_dts(ts, &obj.dts, &out_local, &out_tzoffset)
     obj.value = dtstruct_to_dt64(&obj.dts)
@@ -725,7 +725,7 @@ cdef inline bint _parse_today_now(str val, int64_t* iresult):
         return True
     elif val == 'today':
         # Note: this is *not* the same as Timestamp('today')
-        iresult[0] = Timestamp.utcnow().normalize().value
+        iresult[0] = Timestamp.now().normalize().value
         return True
     return False
 

pandas/tests/indexes/datetimes/test_tools.py

@@ -187,6 +187,48 @@ def test_to_datetime_format_weeks(self, cache):
 
 class TestToDatetime(object):
 
+    def test_to_datetime_now(self):
+        # See GH#18666
+        with tm.set_timezone('US/Eastern'):
+            npnow = np.datetime64('now').astype('datetime64[ns]')
+            pdnow = pd.to_datetime('now')
+            pdnow2 = pd.to_datetime(['now'])[0]
+            # These should all be equal with infinite perf
+            assert abs(pdnow.value - npnow.astype(np.int64)) < 1e10
+            assert abs(pdnow2.value - npnow.astype(np.int64)) < 1e10
+
+            assert pdnow.tzinfo is None
+            assert pdnow2.tzinfo is None
+
+    def test_to_datetime_today(self):
+        # See GH#18666
+        # Test with one timezone far ahead of UTC and another far behind, so
+        # one of these will _almost_ alawys be in a different day from UTC.
+        # Unfortunately this test between 12 and 1 AM Samoa time
+        # this both of these timezones _and_ UTC will all be in the same day,
+        # so this test will not detect the regression introduced in #18666.
+        with tm.set_timezone('Pacific/Auckland'):  # 12-13 hours ahead of UTC
+            nptoday = np.datetime64('today').astype('datetime64[ns]')
+            pdtoday = pd.to_datetime('today')
+            pdtoday2 = pd.to_datetime(['today'])[0]
+            # These should all be equal with infinite perf
+            assert abs(pdtoday.value - nptoday.astype(np.int64)) < 1e10
+            assert abs(pdtoday2.value - nptoday.astype(np.int64)) < 1e10
+
+            assert pdtoday.tzinfo is None
+            assert pdtoday2.tzinfo is None
+
+        with tm.set_timezone('US/Samoa'):  # 11 hours behind UTC
+            nptoday = np.datetime64('today').astype('datetime64[ns]')
+            pdtoday = pd.to_datetime('today')
+            pdtoday2 = pd.to_datetime(['today'])[0]
+            # These should all be equal with infinite perf
+            assert abs(pdtoday.value - nptoday.astype(np.int64)) < 1e10
+            assert abs(pdtoday2.value - nptoday.astype(np.int64)) < 1e10
+
+            assert pdtoday.tzinfo is None
+            assert pdtoday2.tzinfo is None
+
     @pytest.mark.parametrize('cache', [True, False])
     def test_to_datetime_dt64s(self, cache):
         in_bound_dts = [