Use freezegun in DST tests

requirements_test.txt

@@ -9,6 +9,7 @@
 -r requirements_test_pre_commit.txt
 codecov==2.1.12
 coverage==6.1.1
+freezegun==1.1.0
 jsonpickle==1.4.1
 mock-open==1.4.0
 mypy==0.910
@@ -18,6 +19,7 @@ pipdeptree==2.1.0
 pylint-strict-informational==0.1
 pytest-aiohttp==0.3.0
 pytest-cov==2.12.1
+pytest-freezegun==0.4.2
 pytest-socket==0.4.1
 pytest-test-groups==1.0.3
 pytest-sugar==0.9.4

tests/common.py

@@ -371,9 +371,12 @@ def async_fire_mqtt_message(hass, topic, payload, qos=0, retain=False):
 
 @ha.callback
 def async_fire_time_changed(
-    hass: HomeAssistant, datetime_: datetime, fire_all: bool = False
+    hass: HomeAssistant, datetime_: datetime = None, fire_all: bool = False
 ) -> None:
-    """Fire a time changes event."""
+    """Fire a time changed event."""
+    if datetime_ is None:
+        datetime_ = date_util.utcnow()
+
     hass.bus.async_fire(EVENT_TIME_CHANGED, {"now": date_util.as_utc(datetime_)})
 
     for task in list(hass.loop._scheduled):

tests/conftest.py

@@ -9,6 +9,7 @@
 from unittest.mock import MagicMock, patch
 
 from aiohttp.test_utils import make_mocked_request
+import freezegun
 import multidict
 import pytest
 import pytest_socket
@@ -63,15 +64,24 @@ def pytest_configure(config):
 
 
 def pytest_runtest_setup():
-    """Throw if tests attempt to open sockets.
+    """Prepare pytest_socket and freezegun.
+
+    pytest_socket:
+    Throw if tests attempt to open sockets.
 
     allow_unix_socket is set to True because it's needed by asyncio.
     Important: socket_allow_hosts must be called before disable_socket, otherwise all
     destinations will be allowed.
+
+    freezegun:
+    Modified to include https://github.com/spulec/freezegun/pull/424
     """
     pytest_socket.socket_allow_hosts(["127.0.0.1"])
     disable_socket(allow_unix_socket=True)
 
+    freezegun.api.datetime_to_fakedatetime = ha_datetime_to_fakedatetime
+    freezegun.api.FakeDatetime = HAFakeDatetime
+
 
 @pytest.fixture
 def socket_disabled(pytestconfig):
@@ -126,6 +136,43 @@ def __new__(cls, *args, **kwargs):
     socket.socket = GuardedSocket
 
 
+def ha_datetime_to_fakedatetime(datetime):
+    """Convert datetime to FakeDatetime.
+
+    Modified to include https://github.com/spulec/freezegun/pull/424.
+    """
+    return freezegun.api.FakeDatetime(
+        datetime.year,
+        datetime.month,
+        datetime.day,
+        datetime.hour,
+        datetime.minute,
+        datetime.second,
+        datetime.microsecond,
+        datetime.tzinfo,
+        fold=datetime.fold,
+    )
+
+
+class HAFakeDatetime(freezegun.api.FakeDatetime):
+    """Modified to include https://github.com/spulec/freezegun/pull/424."""
+
+    @classmethod
+    def now(cls, tz=None):
+        """Return frozen now."""
+        now = cls._time_to_freeze() or freezegun.api.real_datetime.now()
+        if tz:
+            result = tz.fromutc(now.replace(tzinfo=tz))
+        else:
+            result = now
+
+        # Add the _tz_offset only if it's non-zero to preserve fold
+        if cls._tz_offset():
+            result += cls._tz_offset()
+
+        return ha_datetime_to_fakedatetime(result)
+
+
 def check_real(func):
     """Force a function to require a keyword _test_real to be passed in."""