const mongoose = require('mongoose');

async function withTempDb(dbName, action) {
	const mongoUri	= `mongodb://localhost:27017/${dbName}`;
	const opts	= {useMongoClient: true, promiseLibrary: global.Promise };

	const conn = mongoose.createConnection(mongoUri, opts);							
	const onceOpen = new Promise( resolve => conn.once('open', resolve ));			
	await onceOpen;						

	let result;

	try {
		result = await action(conn);												
	} finally {
		await conn.dropDatabase();
		await conn.close();
	}

	return result;
}

withTempDb('dummy', () => console.log('Sync ok'));

withTempDb('correct', async db => {
	const collection = db.collection('languages');
	await collection.insert({name: 'JS'});
	console.log('correct async okay');
});

withTempDb('tempDB-incorrect', async db => {
	const collection = db.collection('languages');
	collection.insert({name: 'JS'});
	console.log('not waiting for insert result here...');
});