Add force_update to timer integration (#31646)

* force_update added

As per this discussion we need to update last_changed when active timer restarted.
One way to do that is to force HA update the state on each request even if it remains the same.
More details here - https://github.com/home-assistant/architecture/issues/345

* add test for force_update

make sure state_change event fired every time timer (re)started

* remove whitespaces

* remove whitespace

* Update tests/components/timer/test_init.py

Co-Authored-By: Alexei Chetroi <lexoid@gmail.com>

* fix lint

* fix isort

Co-authored-by: Alexei Chetroi <lexoid@gmail.com>

homeassistant/components/timer/__init__.py

@@ -201,6 +201,11 @@ class Timer(RestoreEntity):
         """If entity should be polled."""
         return False
 
+    @property
+    def force_update(self) -> bool:
+        """Return True to fix restart issues."""
+        return True
+
     @property
     def name(self):
         """Return name of the timer."""

tests/components/timer/test_init.py

@@ -33,6 +33,7 @@ from homeassistant.const import (
     ATTR_ID,
     ATTR_NAME,
     CONF_ENTITY_ID,
+    EVENT_STATE_CHANGED,
     SERVICE_RELOAD,
 )
 from homeassistant.core import Context, CoreState
@@ -406,6 +407,47 @@ async def test_timer_restarted_event(hass):
     assert len(results) == 4
 
 
+async def test_state_changed_when_timer_restarted(hass):
+    """Ensure timer's state changes when it restarted."""
+    hass.state = CoreState.starting
+
+    await async_setup_component(hass, DOMAIN, {DOMAIN: {"test1": {CONF_DURATION: 10}}})
+
+    state = hass.states.get("timer.test1")
+    assert state
+    assert state.state == STATUS_IDLE
+
+    results = []
+
+    def fake_event_listener(event):
+        """Fake event listener for trigger."""
+        results.append(event)
+
+    hass.bus.async_listen(EVENT_STATE_CHANGED, fake_event_listener)
+
+    await hass.services.async_call(
+        DOMAIN, SERVICE_START, {CONF_ENTITY_ID: "timer.test1"}
+    )
+    await hass.async_block_till_done()
+    state = hass.states.get("timer.test1")
+    assert state
+    assert state.state == STATUS_ACTIVE
+
+    assert results[-1].event_type == EVENT_STATE_CHANGED
+    assert len(results) == 1
+
+    await hass.services.async_call(
+        DOMAIN, SERVICE_START, {CONF_ENTITY_ID: "timer.test1"}
+    )
+    await hass.async_block_till_done()
+    state = hass.states.get("timer.test1")
+    assert state
+    assert state.state == STATUS_ACTIVE
+
+    assert results[-1].event_type == EVENT_STATE_CHANGED
+    assert len(results) == 2
+
+
 async def test_load_from_storage(hass, storage_setup):
     """Test set up from storage."""
     assert await storage_setup()