Backport the following test from Bitcoin Core
commit a750d77b950175115fcab528fa0d3a2e0ffab96d
Author: John Newbery <john@johnnewbery.com>
Date: Thu Mar 9 17:14:55 2017 -0500
Add tests for mempool persistence
Adds tests for mempool persistence as well as for the new
-persistmempool command line parameter.This is also related:
| * commit 6697a7089441deded836332e7ce3b4a1a9a3cbcd | | Author: Gregory Sanders <gsanders87@gmail.com> | | Date: Wed Dec 6 12:08:40 2017 -0500 | | | | add test for unconfirmed balance between restarts