Can you run the unikernel under a debugger when testing? Can you get crash dumps? Stack backtraces?
Unless you're running your unikernel on bare metal, it's still running under an OS. It's just that the OS is called a hypervisor and is less bloated than most OSs.
That works even on bare metal if the network works. Similarly, there are remote system calls that can be used for netstat and such. I don't think there is a good way to secure them in many environments at this point, but adding spipe might not be too hard.
https://github.com/rumpkernel/rumpctrl
There is also frankenlibc where you can run the application as an actual userland process (but still with the rump kernel) under a variety of operating systems. I think applications that run on one (frankenlibc or rumprun) should be able to run on the other without changes (other than build related).
https://github.com/justincormack/frankenlibc/
I'm not sure if NetBSD's kernel debugger or crash dumps work with rump kernels at this point. I haven't played with them myself yet, just keeping an eye on what other folks are doing. And yes, hypervisors also have debugging tools.
Unless you're running your unikernel on bare metal, it's still running under an OS. It's just that the OS is called a hypervisor and is less bloated than most OSs.