firebase functions: Unit test for storage onFinalize()

How can I write a unit test for the following firebase function: => {
return storage
      .then(() => console.log(`Deletion successful: '${}'`))
      .catch(err => console.error(err));

I read the docs and setup a unit test for the 'online mode', connecting to a test project.

My approach is to write an assertion whether "Deletion successful" has been logged. I think the current unit test fails silently (I dont see any errors besides my failing assertion) because the provided does not really exists so the file cant be found.

Do I have to create and upload this file before the test/ how can I mock it?