If you use the the Admin Create Ticket feature, you have to choose a ticket type. If you use a service catalog to create a ticket, there will be pre-assigned default ticket type in the service catalog. You can change it when you create the test ticket. If you leave it blank, it defaults to Service Request.
Routing Rules can override this.
Here is an idea:
You could create a "Testing" Ticket Type and create a routing rule to look for the keyword "test" in the title and assign it to the type "Testing"