Test an MQTT Automation With a Fictional Event Before Relying on It

Description and use

Testing an MQTT automation with a fictional event confirms that the topic, payload filter, and action work together before relying on it in production.

Problem

Verify that an MQTT automation processes a message correctly before relying on it in production.

Outcome

The automation successfully processed a fictional MQTT message, creating a notification and trace, confirming the topic, payload filter, and action work together.

Workflow

• 1. Write a clear claim: a JSON message on lab/automation-test/2026-10-31/event with event_type new_device should create a persistent notification.
• 2. Create a test topic under a controlled prefix, e.g., lab/automation-test/2026-10-31/event.
• 3. Define a Home Assistant automation with a narrow match: trigger on the test topic, value_template extracting event_type, payload condition equals new_device, action persistent_notification.create.
• 4. Publish a fictional JSON payload to the test topic using Home Assistant’s MQTT Publish tool or another publisher: {"event_type":"new_device","name":"Tutorial printer","ip":"192.0.2.42","note":"fictional test data"}.
• 5. Verify the persistent notification appears and check the automation trace for the trigger data and action result.
• 6. Perform a negative test by publishing a message with event_type device_offline to ensure the automation does not run.
• 7. Optionally test restarts by restarting Home Assistant and inspecting trace timestamps to confirm no false positives from retained messages.
• 8. Once tests pass, move the automation to a real integration, keeping the first production action observational.

Evidence

An MQTT automation can look finished before it has processed a single message from a broker.

Source

Use a topic reserved for testing, data that identifies no real person or device, and a harmless action you can see.

Source

Publish once to the exact test topic with this payload: {"event_type":"new_device","name":"Tutorial printer","ip":"192.0.2.42","note":"fictional test data"}.

Source