test.js

async function sleep(time) {
	return new Promise((resolve) => setTimeout(resolve, time));
}

async function PromiseAll(args) {
	args.forEach(async func => {
		await func();
	});
} 

async function test1(delay) {
	console.log('a1');

	await sleep(delay);
	console.log('b1');

	await sleep(delay);
	console.log('c1');
}

async function test2(delay) {
	console.log('a2');

	await sleep(delay);
	console.log('b2');

	await sleep(delay);
	console.log('c2');
}

async function main() {
	console.log('start');
	await Promise.all([test1(100), test2(100)]);
	//await PromiseAll([test1(100), test2(100)])
	console.log('end');
}

main();