Do you need separate ICS instances to do DEV/TEST/PROD?

Summary

Do you need separate ICS instances to do DEV/TEST/PROD?

Content

I read the FAQ's about moving your integrations through different environments, but I am unclear on what needs to be procured to do so.  It seems that a cloud environment is an entire instance of ICS.  Is there any way to share ICS environments between test instances? Does an entire ICS instance need to be launched for each test environment?

Thanks!