React jest test, unable to test a method 'TypeError: ... is not a function'

not the full code but similar idea:

implementaion.tsx:

export const provider: React.FC<{}> = ({
  children,
}) => {
 const handleDiscard = React.useCallback(() => {
    invokeDiscard();
    ...
  }, [invokeDiscard]);
}

implementaion.test.tsx:

const actual = require("./implementation");

it("discards") {
  act(() => {actual.handleDiscard()});
  expect(invokeDiscard).toHaveBeenCalled();
}

TypeError: actual.handleDiscardis not a function

why???