tests: use communicate() instead wait()

[igaw]

Tests written Python should be updated. There are many calls to Popen.wait() which is deprecated:

This will deadlock when using stdout=PIPE or stderr=PIPE and the child process generates enough output to a pipe such > that it blocks waiting for the OS pipe buffer to accept more data. Use Popen.communicate() when using pipes to avoid that.

        proc = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE,
                                encoding='utf-8')
        return proc.wait()

see Python documentation on wait: https://docs.python.org/3/library/subprocess.html#subprocess.Popen.wait

[martin-belanger]

NOTE: There is also subprocess.run() that can be used to start a process and wait for it to complete.
https://docs.python.org/3/library/subprocess.html#using-the-subprocess-module

[igaw]

Ah yes. I think anything is better than the wait(). I had fun in the past with this one.

(and there is also the funky asyncio thingy, but that seems way to complex and over engineered.)