helper to test custom hook (especially if it's using useEffect) with React, Jest & Enzyme

customHookTestHelper.js

import React from "react";
import { isFunction } from "lodash";
import { mount } from "enzyme";

export default (hook, props) => {
    let wrapper, hookResult, hookParams, error;

    if (isFunction(props)) {
        hookParams = props;
        props = {};
    }

    const Comp = (props) => {
        try {
            hookResult = hook(...(hookParams ? hookParams() : [props]));
        }
        catch (ex) {
            error = ex;
        }

        return null;
    };

    //have to use mount() because shallow() doesnt support useEffect - https://github.com/airbnb/enzyme/issues/2086
    wrapper = mount(<Comp {...props} />);

    return {
        wrapper,
        getHookResult: () => hookResult,
        getError: () => error,
    };
};

myCustomHook.js

import { useEffect } from "react";
import { registerToServiceEvent, unRegisterFromServiceEvent} from "services/myService";

const myCustomHook = (p1, p2) => {
	
	useEffect(() => {
		registerToServiceEvent(p1, p2);
		
		return () => {
			unRegisterFromServiceEvent(p1, p2);
		};
	}, [p1, p2]);	
	
	return "value";
};

myCustomHook.test.js

jest.mock("services/myService", ()=>({
	registerToServiceEvent: jest.fn(),
	unRegisterFromServiceEvent:jest.fn(),
}));

import { registerToServiceEvent, unRegisterFromServiceEvent} from "services/myService";

it("should run my custom hook", () => {
	const param1 = "a",
		  param2 = "b";
	
	const { getHookResult } = testCustomHook(() => myCustomHook(param1, param2));
	
	expect(getHookResult()).toBe("value");
	expect(registerToServiceEvent).toHaveBeenCalledWith(param1, param2);
    expect(unRegisterFromServiceEvent).toHaveBeenCalledWith(param1, param2);
});