Mock function call inside other function

How to mock a function call inside another function in JavaScript?

Code example:

returnNumber.js

export default function returnNumber() {
  return 5;
}

myFunction.js

import returnNumber from "./returnNumber";

export default function myFunction(input) {
  return input + returnNumber();
}

I would like to test it by doing something like this, but none if the code examples I saw seem to be working in my case

import myFunction from "./myFunction";

test("myFunction should equal 6", async () => {
  returnNumber = () => {
    return 1
  }

  expect(myFunction(5)).toEqual(6);
});

Considering the example above; can I test myFunction while overriding returnNumber’s return value?