anchor.diff:  
   let
     configDir = "/var/lib/foobar";
  +  mqttUsername = "homeassistant";
     mqttPassword = "secret";
   in {
     name = "home-assistant";
  
positive.code:           elevation = 0;
          };
          frontend = {};
          # uses embedded mqtt broker
          mqtt.password = mqttPassword;
          binary_sensor = [{
            platform = "mqtt";
            state_topic = "home-assistant/test";
  
negative.code:     with subtest("Toggle a binary sensor using MQTT"):
          # wait for broker to become available
          hass.wait_until_succeeds(
              "mosquitto_sub -V mqttv311 -t home-assistant/test -u ${mqttUsername} -P '${mqttPassword}' -W 1 -t '*'"
          )
          hass.succeed(
              "mosquitto_pub -V mqttv311 -t home-assistant/test -u ${mqttUsername} -P '${mqttPassword}' -m let_there_be_light"
          )
      with subtest("Print log to ease debugging"):
          output_log = hass.succeed("cat ${configDir}/home-assistant.log")
  