I use this to check if the test process has started:

````python
        # Test backend/frontend write and flush a line to stdout
        # that we know when they are ready.
        proc.stdout.readline()
````
On one python version the test processes would not print the line and the test would hang. I had to kill the process to get the stdout/err to find out what the problem was. After I fixed, that the deferred kill isn't needed, but I left it, should I remove it? I'll add a comment.