Verifying a PITR

What would be the best way to verify that a PITR came up with *all*
the expected data?

This is mostly for a controlled failover, where I manually bring down
the primary server, and shouldn't ever lose a transaction.
If I need to use something like txid_current(), how do I ensure that
it's the last transaction before shutdown, and the first after
recovery?

Thanks
-jim