Add file validation to savemempool RPC test

test/functional/mempool_persist.py

@@ -149,8 +149,9 @@ class MempoolPersistTest(BitcoinTestFramework):
         mempooldat1 = os.path.join(self.nodes[1].datadir, self.chain, 'mempool.dat')
         self.log.debug("Remove the mempool.dat file. Verify that savemempool to disk via RPC re-creates it")
         os.remove(mempooldat0)
-        self.nodes[0].savemempool()
+        result0 = self.nodes[0].savemempool()
         assert os.path.isfile(mempooldat0)
+        assert_equal(result0['filename'], mempooldat0)
 
         self.log.debug("Stop nodes, make node1 use mempool.dat from node0. Verify it has 6 transactions")
         os.rename(mempooldat0, mempooldat1)