Do you really need Jest?

declaw-jest.ts

/**
 * If you wish to break free from the embrace->extend->imprison paradigm of Jest, this little Adapter can help you gradually break free.
 * Use these methods along with the generic statements like xdescribe instead of describe.skip ('it', 'fit', 'xit', instead of 'test')
 * Create your new tests using these adapters, and over time swap out your Jest specific calls in existing tests.
 * Once your project is fully converted, you can simply replace Jasmine for Jest inside your package.json and all your tests should still be green.
 *
 * Jest+Yarn+jsdom expose your project to almost 4,000 currently open issues, and 400ish open PRs (somebody spent personal time to submit a fix, but it is still being ignored).
 * For Node.js based applications, I personally just don't see the need for Jest.
 *
 * On a related note if you add CRA into the mix, you get an *additional* 2,000ish open issues and *another* 400ish open PRs.
 * If the purpose of testing is to ensure stability, and if your UI tests really do take an excessive amount of time using the same environment your users actually use,
 * perhaps a better strategy would be to set up a few machines each configured to run a portion of your test files.
 *
 * FUTURE:
 * I may add Mocha in here, and am open to suggestions for other helpful cross-environment adapter functions.
 * All my projects are TypeScript, but if there is any real interest here, I'll update this gist with a pure JavaScript version.
 *
 * FAIR WARNING!
 * I've been using this code for a couple of years.
 * However, when I decided to post this gist, I added the 3 "tick" functions at the bottom.
 * I have never used the tick functions and don't actually know if they work :-)
 * Furthermore, they require at least Jest 26 to work.
 *
 * This is free and unencumbered software released into the public domain to be used however you wish.
 * Specifically it is released under "The Unlicense" <http://unlicense.org/> as defined on 2022/02/19
 */
declare var jest;

/**
 * Set the timeout value for when a "hung" test is considered to have failed
 */
export function setTestTimeout(ms: number) {
	if (typeof jest !== 'undefined') {
		if (typeof ms === 'number')
			jest.setTimeout(ms);
	}
	else {
		let originalTimeout = jasmine.DEFAULT_TIMEOUT_INTERVAL;
		beforeAll(function() {
			jasmine.DEFAULT_TIMEOUT_INTERVAL = ms;
		});
		afterAll(function() {
			jasmine.DEFAULT_TIMEOUT_INTERVAL = originalTimeout;
		});
	}
}

/**
 * Create a simple function that when invoked will record its arguments and return value for each invocation.
 *
 * @param impl  An optional delegate/callback to perform user specified operations.
 */
export function createFnSpy(impl?: (...args: any[]) => any) {
	if (typeof jest !== 'undefined')
		return jest.fn(impl);
	else {
		let retVal = jasmine.createSpy('spy', impl);
		if (impl) {
			retVal = retVal.and.callFake((...args: any[]) => {
				return impl(...args);
			});
		}
		return retVal;
	}
}

/**
 * Wrap the specified method of an object and return a spy for that object.
 */
export function spyOnObject(obj: any, methodName: string) {
	if (typeof jest !== 'undefined')
		return jest.spyOn(obj, methodName);
	else
		return spyOn(obj, methodName).and.callThrough();
}

/**
 * Retrieve the arguments for all (or a specific) invocation(s) of a spy function or object method
 */
export function spyCallArguments(spy: any, invocationIdx?: number) {
	if (typeof jest !== 'undefined') {
		if (typeof invocationIdx === 'number' && invocationIdx >= 0)
			return spy.mock?.calls?.[invocationIdx];
		return spy.mock?.calls;
	}
	else {
		if (typeof invocationIdx === 'number' && invocationIdx >= 0)
			return spy.calls?.argsFor(invocationIdx);
		return spy.calls?.allArgs();
	}
}

/**
 * Retrieve the results of all (or a specific) invocation(s) of a spy function or object method.
 */
export function spyCallResult(spy: any, invocationIdx?: number) {
	if (typeof jest !== 'undefined') {
		if (typeof invocationIdx === 'number' && invocationIdx >= 0)
			spy.mock?.results?.[invocationIdx]?.value;
		return spy.mock?.results?.map(m => m.value);
	}
	else {
		if (typeof invocationIdx === 'number' && invocationIdx >= 0)
			return spy.calls?.all()[invocationIdx]?.returnValue;
		return spy.calls?.all().map(m => m.returnValue);
	}
}

/**
 * Exit a test with a specific failure.
 */
export function failTest(err: string | Error, done?: (e?: Error) => void) {
	if (typeof jest !== 'undefined') {
		if (typeof err === 'string')
			err = new Error(err);
		if (typeof done === 'function')
			done(err);
		else
			throw err;
	}
	else {
		fail(err);
		if (typeof done === 'function')
			done();
	}
}

/**
 * Stop the system clock from automatically advancing.
 * WARNING: Don't forget to ensure @see resumeTicks is called to undo the effects of this function.
 * @param date  Optionally set the system time to a specific Date.
 */
export function suspendTicks(date?: Date) {
	if (typeof jest !== 'undefined') {
		jest.useFakeTimers();
		if (date)
			jest.setSystemTime(date.getTime());
	}
	else {
		jasmine.clock().install();
		if (date)
			jasmine.clock().mockDate(date);
	}
}

/**
 * Advance the system clock by the specified number of milliseconds.
 */
export function advanceTicks(ms: number) {
	if (typeof jest !== 'undefined') {
		jest.advanceTimersByTime(ms);
	}
	else {
		jasmine.clock().tick(ms);
	}
}

/**
 * Undo the effects of @see suspendTicks
 */
export function resumeTicks() {
	if (typeof jest !== 'undefined') {
		jest.useRealTimers();
	}
	else {
		jasmine.clock().uninstall();
	}
}