Tests: Use UTC-based utcnow().date() instead of local date.today()

`datetime.date.today()` returns the current local date. So, its outcome
depends on the system time zone. Because we want to use UTC-based date
and time objects instead, `datetime.utcnow().date()` is a better choice.

setup.py

@@ -70,6 +70,7 @@ def read(path):
               'zope.testing>=4,<5',
               'zope.testrunner>=5,<6',
               'zc.customdoctests>=1.0.1,<2',
+              'time-machine>=2,<3',
               'createcoverage>=1,<2',
               'stopit>=1.1.2,<2',
               'flake8>=4,<5'],

src/crate/client/sqlalchemy/doctests/itests.txt

@@ -105,7 +105,7 @@ aren't set when the row is inserted as there is no default method::
 
 The datetime and date can be set using a update statement::
 
-    >>> location.nullable_date = datetime.today()
+    >>> location.nullable_date = datetime.utcnow().date()
     >>> location.nullable_datetime = datetime.utcnow()
     >>> session.flush()
 

src/crate/client/tests.py

@@ -27,7 +27,7 @@
 import unittest
 import doctest
 from pprint import pprint
-from datetime import datetime, date
+from datetime import datetime
 from http.server import HTTPServer, BaseHTTPRequestHandler
 import ssl
 import time
@@ -213,7 +213,7 @@ class Location(Base):
         __tablename__ = 'locations'
         name = sa.Column(sa.String, primary_key=True)
         kind = sa.Column(sa.String)
-        date = sa.Column(sa.Date, default=date.today)
+        date = sa.Column(sa.Date, default=lambda: datetime.utcnow().date())
         datetime_tz = sa.Column(sa.DateTime, default=datetime.utcnow)
         datetime_notz = sa.Column(sa.DateTime, default=datetime.utcnow)
         nullable_datetime = sa.Column(sa.DateTime)

src/crate/testing/test_datetime.py

@@ -0,0 +1,90 @@
+# -*- coding: utf-8; -*-
+#
+# Licensed to CRATE Technology GmbH ("Crate") under one or more contributor
+# license agreements.  See the NOTICE file distributed with this work for
+# additional information regarding copyright ownership.  Crate licenses
+# this file to you 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.
+#
+# However, if you have executed another commercial license agreement
+# with Crate these terms will supersede the license and you may use the
+# software solely pursuant to the terms of the relevant commercial agreement.
+
+import os
+import sys
+import unittest
+from datetime import datetime, date
+from unittest import TestCase, mock
+
+import time_machine
+
+
+class DateTodayTest(TestCase):
+    """
+    `date.today()` returns the current local date, as advertised in the
+    documentation [1]. Thus, it depends on the system time zone.
+
+    The following test cases demonstrate that the test suite previously
+    failed around midnight, where the UTC vs. non-UTC days overlapped,
+    and when running on machines with non-UTC time zone.
+
+    On the other hand, `datetime.utcnow().date()` works equally well in all
+    situations, so we want to use that within the SQLAlchemy test cases.
+
+    Funny enough, the problem is not observable on Linux?
+
+    [1] https://docs.python.org/3/library/datetime.html#datetime.date.today
+    """
+
+    @mock.patch.dict(os.environ, {"TZ": "UTC"})
+    @time_machine.travel("2022-07-22T00:42:00+0200")
+    def test_date_today_depends_on_system_timezone_success_on_utc(self):
+        today_local = date.today()
+        today_utc = datetime.utcnow().date()
+        self.assertEqual(today_local, today_utc)
+        self.assertEqual(today_local, date(2022, 7, 21))
+        self.assertEqual(today_utc, date(2022, 7, 21))
+
+    @unittest.skipIf(sys.platform == "linux", "Problem not observable on Linux")
+    @mock.patch.dict(os.environ, {"TZ": "Europe/Prague"})
+    @time_machine.travel("2022-07-22T00:42:00+0200")
+    def test_date_today_depends_on_system_timezone_failure_on_non_utc(self):
+        today_local = date.today()
+        today_utc = datetime.utcnow().date()
+        self.assertNotEqual(today_local, today_utc)
+        self.assertEqual(today_local, date(2022, 7, 22))
+        self.assertEqual(today_utc, date(2022, 7, 21))
+
+    @mock.patch.dict(os.environ, {"TZ": "UTC"})
+    @time_machine.travel("2022-07-22T00:42:00+0200")
+    def test_date_today_utc(self):
+        today_local = date.today()
+        self.assertEqual(today_local, date(2022, 7, 21))
+
+    @unittest.skipIf(sys.platform == "linux", "Problem not observable on Linux")
+    @mock.patch.dict(os.environ, {"TZ": "Europe/Prague"})
+    @time_machine.travel("2022-07-22T00:42:00+0200")
+    def test_date_today_non_utc(self):
+        today_local = date.today()
+        self.assertEqual(today_local, date(2022, 7, 22))
+
+    @mock.patch.dict(os.environ, {"TZ": "UTC"})
+    @time_machine.travel("2022-07-22T00:42:00+0200")
+    def test_utcnow_date_utc(self):
+        today_utc = datetime.utcnow().date()
+        self.assertEqual(today_utc, date(2022, 7, 21))
+
+    @mock.patch.dict(os.environ, {"TZ": "Europe/Prague"})
+    @time_machine.travel("2022-07-22T00:42:00+0200")
+    def test_utcnow_date_non_utc(self):
+        today_utc = datetime.utcnow().date()
+        self.assertEqual(today_utc, date(2022, 7, 21))

src/crate/testing/tests.py

@@ -24,6 +24,8 @@
 import unittest
 import doctest
 import tempfile
+
+from .test_datetime import DateTodayTest
 from .test_layer import LayerUtilsTest
 
 
@@ -64,4 +66,5 @@ def test_suite():
     )
     suite.addTest(s)
     suite.addTest(unittest.makeSuite(LayerUtilsTest))
+    suite.addTest(unittest.makeSuite(DateTodayTest))
     return suite