Urgent! I want to travel to Singapore, where my friend found a tourist visa guaranteed by Singaporeans, but I only bought a one-way ticket and didn't want to buy a round trip.

You will be checked when you leave China airport. If you don't have a return ticket, you will be suspected of staying in Singapore and have an immigration tendency. You will not be allowed to board the plane. You'd better buy a return ticket. The date of the return ticket must be before the visa expires, otherwise it will be useless.