run-tests: fix race condition Before this patch, it was possible for run-tests to crash on a race condition. The race condition happens in the following case: - the last test finishes and calls: done.put(None) - the context switches to the main thread that clears the channels list - the context switches to the last test mentioned above, it tries to access channels[channel] and crashes This happened to me while running run-tests. This patch fixes the issue by clearing the channel before considering that the test is done.