await server.stop();
 try {
 const r = await db.things.insertOne({ a: 1 }); //no error, r is undefined
 } catch (err) {
 console.log(err); 
 }
 await server.restart();
 const r = await db.things.insertOne({ a: 1 });
 assert(r.insertedCount === 1); //it works

 db.things.insertOne({ a: 1 }, (err, result) => {
 if (err) { //"MongoTimeoutError" "Server selection timed out after 10000 ms"
 return reject(err);
 }
 resolve(result);
 })