Jest: How to test function that returns a function

I have several functions I would like to test with Jest. All functions are functions that return functions.

A simple example:

export function csl(foo) {
  return function(bar) {
      return(bar)
     };
}

now I want to test if the input = the return is. I try it with:

  expect(() => csl("foo")).toBe("foo") // = received: [Function anonymous]

  expect(csl("foo")).toBe("foo") // = received: undefined

How I can test these functions?