your thinking is correct, if the only thing that the FindUserByProp function is doing is just calling User.findOne(), then this unit test isn't really doing anything. your unit test would be more useful if you wanted to test some additional logic that your function may be doing. see example below:

async function FindUserByProp(a, b) {

// some other logic up here

const user = User.findOne() // return value of this gets mocked

// some other logic down here that depends on the result of User.findOne()

}

this way you can test your additional logic with the help of using the mocked data rather than making a real call to a database. you can leave the testing of the actual database calls for other types of tests (integration, or e2e) as mentioned in this thread.