callstack__react-native-testing-library/src/render-hook.tsx

import React from 'react';
import type { ComponentType } from 'react';
import { renderInternal } from './render';

export type RenderHookResult<Result, Props> = {
  rerender: (props: Props) => void;
  result: { current: Result };
  unmount: () => void;
};

export type RenderHookOptions<Props> = {
  initialProps?: Props;
  wrapper?: ComponentType<any>;
};

export function renderHook<Result, Props>(
  renderCallback: (props: Props) => Result,
  options?: RenderHookOptions<Props>,
): RenderHookResult<Result, Props> {
  const initialProps = options?.initialProps;
  const wrapper = options?.wrapper;

  const result: React.MutableRefObject<Result | null> = React.createRef();

  function TestComponent({ renderCallbackProps }: { renderCallbackProps: Props }) {
    const renderResult = renderCallback(renderCallbackProps);

    React.useEffect(() => {
      result.current = renderResult;
    });

    return null;
  }

  const { rerender: baseRerender, unmount } = renderInternal(
    // @ts-expect-error since option can be undefined, initialProps can be undefined when it should'nt
    <TestComponent renderCallbackProps={initialProps} />,
    {
      wrapper,
    },
  );

  function rerender(rerenderCallbackProps: Props) {
    return baseRerender(<TestComponent renderCallbackProps={rerenderCallbackProps} />);
  }

  // @ts-expect-error result is ill typed because ref is initialized to null
  return { result, rerender, unmount };
}