Bruno,
I am not very clear with your question; in case you meant that you have the Test Tenant and you request for a Productive Tenant, they will both have different URL as they will both be alive until you terminate the Test Tenant.
In case you mean that you are already on the Productive Tenant and you want to proceed with a Change Project and request the corresponding Test Tenant, answer is the same, you will receive a second URL.
Kindly confirm whether this answers your question or, let me know and I will try helping you again 
Regards.
Alejandro.