[light] Add integration test for ToggleAction

tests/integration/fixtures/light_toggle_action.yaml

@@ -0,0 +1,37 @@
+esphome:
+  name: light-toggle-action-test
+host:
+api:
+logger:
+  level: DEBUG
+
+output:
+  - platform: template
+    id: test_out
+    type: float
+    write_action:
+      - lambda: ""
+
+light:
+  - platform: monochromatic
+    name: "Test Light"
+    id: test_light
+    output: test_out
+    default_transition_length: 0s
+
+button:
+  # Test 1: light.toggle without transition_length (HasTransitionLength=false)
+  - platform: template
+    id: btn_toggle
+    name: "Toggle"
+    on_press:
+      - light.toggle: test_light
+
+  # Test 2: light.toggle with transition_length (HasTransitionLength=true)
+  - platform: template
+    id: btn_toggle_with_trans
+    name: "Toggle With Trans"
+    on_press:
+      - light.toggle:
+          id: test_light
+          transition_length: 0s

tests/integration/test_light_toggle_action.py

@@ -0,0 +1,58 @@
+"""Integration test for light::ToggleAction.
+
+Tests both ToggleAction<HasTransitionLength=false> and
+ToggleAction<HasTransitionLength=true> instantiations.
+"""
+
+import asyncio
+from typing import Any
+
+import pytest
+
+from .types import APIClientConnectedFactory, RunCompiledFunction
+
+
+@pytest.mark.asyncio
+async def test_light_toggle_action(
+    yaml_config: str,
+    run_compiled: RunCompiledFunction,
+    api_client_connected: APIClientConnectedFactory,
+) -> None:
+    """Test light.toggle with and without transition_length."""
+    async with run_compiled(yaml_config), api_client_connected() as client:
+        state_futures: dict[int, asyncio.Future[Any]] = {}
+
+        def on_state(state: Any) -> None:
+            if state.key in state_futures and not state_futures[state.key].done():
+                state_futures[state.key].set_result(state)
+
+        client.subscribe_states(on_state)
+
+        entities = await client.list_entities_services()
+        light = next(e for e in entities[0] if e.object_id == "test_light")
+        buttons = {e.name: e for e in entities[0] if hasattr(e, "name")}
+
+        async def wait_for_state(key: int, timeout: float = 5.0) -> Any:
+            loop = asyncio.get_running_loop()
+            state_futures[key] = loop.create_future()
+            try:
+                return await asyncio.wait_for(state_futures[key], timeout)
+            finally:
+                state_futures.pop(key, None)
+
+        async def press_and_wait(button_name: str) -> Any:
+            btn = buttons[button_name]
+            client.button_command(btn.key)
+            return await wait_for_state(light.key)
+
+        # Test 1: toggle without transition_length flips off->on
+        state = await press_and_wait("Toggle")
+        assert state.state is True
+
+        # Test 2: toggle with transition_length flips on->off
+        state = await press_and_wait("Toggle With Trans")
+        assert state.state is False
+
+        # Test 3: toggle without transition_length flips off->on again
+        state = await press_and_wait("Toggle")
+        assert state.state is True