wrapperComponent.ts

function setup(...args) {
  const returnVal = {};
  function ComponentHarness() {
    // change the object referenced by returnVal, otherwise we would lose the reference in the outer scope and could not make assertions on the values returned by the hook
    Object.assign(returnVal, myCustomHook(...args));
    return null;
  }

  render(<ComponentHarness />);

  return returnVal;
}