How to to force a process to have high CPU

I have a service that monitors how much CPU a process is using and alarms when the process is above a certain threshold.

I need to test to see that the monitor is detecting that the service is using a large amount of CPU cycles.

Is there any way to force a process to show a high amount of CPU usage without having access to the source code on the process?

I would eventually like to have a testing application that could spike the CPU of any process.