Merge bitcoin/bitcoin#29973: test: Assumeutxo: ensure failure when importing a snapshot twice

b259b0e [Test] Assumeutxo: ensure failure when importing a snapshot twice (Alfonso Roman Zubeldia)

Pull request description:

  I am getting familiar with the `assume_utxo` tests and I found that the scenario of trying to activate a snapshot twice is not covered. This test is to ensure failure when loading a snapshot if there is already a snapshot-based chainstate.

ACKs for top commit:
  fjahr:
    Code review ACK b259b0e
  kevkevinpal:
    tACK [b259b0e](bitcoin/bitcoin@b259b0e)
  achow101:
    ACK b259b0e
  rkrux:
    tACK [b259b0e](bitcoin/bitcoin@b259b0e)

Tree-SHA512: 3510861390d0e40cdad6861b728df04827a1b63e642f3d956aee66ed2770b1cb7e3aa3eb00c62eb9da0544703c943cc5296936c9ebfcac18c719741c354421bb

Author: achow101

test/functional/feature_assumeutxo.py

@@ -405,6 +405,10 @@ def check_tx_counts(final: bool) -> None:
         assert_equal(snapshot['snapshot_blockhash'], dump_output['base_hash'])
         assert_equal(snapshot['validated'], False)
 
+        self.log.info("Check that loading the snapshot again will fail because there is already an active snapshot.")
+        with n2.assert_debug_log(expected_msgs=["[snapshot] can't activate a snapshot-based chainstate more than once"]):
+            assert_raises_rpc_error(-32603, "Unable to load UTXO snapshot", n2.loadtxoutset, dump_output['path'])
+
         self.connect_nodes(0, 2)
         self.wait_until(lambda: n2.getchainstates()['chainstates'][-1]['blocks'] == FINAL_HEIGHT)
         self.sync_blocks()