[$] Testing and the stable tree

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The stable tree was the topic for a plenary session led by Sasha Levin at
the 2019 Linux Storage, Filesystem, and Memory-Management Summit (LSFMM).
One of the main areas that needs attention is testing, according to Levin.
He wanted to discuss how to do more and better testing as well as to
address any concerns that attendees might have with regard to the stable tree.