esphome/tests/components/logger/common-default_uart.yaml

esphome:
  on_boot:
    then:
      - logger.log:
          level: warn
          format: "Warning: Logger level is %d"
          args: [id(logger_id).get_log_level()]
      - logger.set_level: WARN

logger:
  id: logger_id
  level: DEBUG
  initial_level: INFO

select:
  - platform: logger
    name: Logger Level