Reorganize trigger code (#38655)

tests/helpers/test_trigger.py

@@ -0,0 +1,12 @@
+"""The tests for the trigger helper."""
+import pytest
+import voluptuous as vol
+
+from homeassistant.helpers.trigger import async_validate_trigger_config
+
+
+async def test_bad_trigger_platform(hass):
+    """Test bad trigger platform."""
+    with pytest.raises(vol.Invalid) as ex:
+        await async_validate_trigger_config(hass, [{"platform": "not_a_platform"}])
+    assert "Invalid platform 'not_a_platform' specified" in str(ex)