need help for yaml file

[west spruce]

For templates... Use platform: template not test

Though that's not the preferred syntax - it should be

template:
  - sensor:
      - name: "test"
        unit_of_measurement: "merci" 
        state: >
          {{15}}

Your version with the % is for internal variables and never has an output (double brackets), so would never have a state, even if it was set up properly

[boreal oriole]

ok I edit like that

template:
  - sensor:
    name: test
    unit_of_measurement: "helloword"
    state: >
      {{15}}

i suppose I had to change test: !include test.yaml to template: !include test.yaml in template.yaml no ?

[west spruce]

If you are doing it through an include you need to remove the template from the start of the file

[boreal oriole]

?