And indeed also very useful for testing. "what happens if we simulate this process being a bit slow" - send it a SIGSTOP. Doing so can simulate a number of other weird cases too as observed from the outside , such as a process trashing on swap, NFS hanging.
I've found that doing that to etcd causes other etcd in the cluster to randomly hang - while it handles a lot of other failures fine (instant poweroff, network partitioning, randomly crash etcd, sending SIGSTOP to on member of a cluster breaks everything - I don't know if that's improved since I did those tests though)
As I usually have to point out, Ctrl-Z sends SIGTSTP, which can be caught by a signal handler – unlike SIGSTOP, which is not sent by any key in the terminal driver, and which can not be caught by a signal handler.
I've found that doing that to etcd causes other etcd in the cluster to randomly hang - while it handles a lot of other failures fine (instant poweroff, network partitioning, randomly crash etcd, sending SIGSTOP to on member of a cluster breaks everything - I don't know if that's improved since I did those tests though)