tests: Check that the last hardened cache upgrade occurs

When loading an older wallet without the last hardened cache, an
automatic upgrade should be performed. Check this in
wallet_backwards_compatibility.py

When migrating a wallet, the migrated wallet should always have the last
hardened cache, so verify in wallet_migration.py

test/functional/wallet_backwards_compatibility.py

@@ -21,9 +21,11 @@ import shutil
 from test_framework.blocktools import COINBASE_MATURITY
 from test_framework.test_framework import BitcoinTestFramework
 from test_framework.descriptors import descsum_create
+from test_framework.messages import ser_string
 
 from test_framework.util import (
     assert_equal,
+    assert_greater_than,
     assert_raises_rpc_error,
 )
 
@@ -149,18 +151,13 @@ class BackwardsCompatibilityTest(BitcoinTestFramework):
         assert_equal(bad_deriv_wallet_master.getaddressinfo(bad_path_addr)["hdkeypath"], good_deriv_path)
         bad_deriv_wallet_master.unloadwallet()
 
-        # If we have sqlite3, verify that there are no keymeta records
-        try:
-            import sqlite3
-            wallet_db = node_master.wallets_path / wallet_name / "wallet.dat"
-            conn = sqlite3.connect(wallet_db)
-            with conn:
-                # Retrieve all records that have the "keymeta" prefix. The remaining key data varies for each record.
-                keymeta_rec = conn.execute("SELECT value FROM main where key >= x'076b65796d657461' AND key < x'076b65796d657462'").fetchone()
-                assert_equal(keymeta_rec, None)
-            conn.close()
-        except ImportError:
-            self.log.warning("sqlite3 module not available, skipping lack of keymeta records check")
+        def check_keymeta(conn):
+            # Retrieve all records that have the "keymeta" prefix. The remaining key data varies for each record.
+            keymeta_rec = conn.execute(f"SELECT value FROM main where key >= x'{ser_string(b'keymeta').hex()}' AND key < x'{ser_string(b'keymetb').hex()}'").fetchone()
+            assert_equal(keymeta_rec, None)
+
+        wallet_db = node_master.wallets_path / wallet_name / "wallet.dat"
+        self.inspect_sqlite_db(wallet_db, check_keymeta)
 
     def test_ignore_legacy_during_startup(self, legacy_nodes, node_master):
         self.log.info("Test that legacy wallets are ignored during startup on v29+")
@@ -342,6 +339,13 @@ class BackwardsCompatibilityTest(BitcoinTestFramework):
             # Remove the wallet from old node
             wallet_prev.unloadwallet()
 
+            # Open backup with sqlite and get flags
+            def get_flags(conn):
+                flags_rec = conn.execute(f"SELECT value FROM main WHERE key = x'{ser_string(b'flags').hex()}'").fetchone()
+                return int.from_bytes(flags_rec[0], byteorder="little")
+
+            old_flags = self.inspect_sqlite_db(backup_path, get_flags)
+
             # Restore the wallet to master
             load_res = node_master.restorewallet(wallet_name, backup_path)
 
@@ -378,6 +382,21 @@ class BackwardsCompatibilityTest(BitcoinTestFramework):
 
             wallet.unloadwallet()
 
+            # Open the wallet with sqlite and inspect the flags and records
+            def check_upgraded_records(conn, old_flags):
+                flags_rec = conn.execute(f"SELECT value FROM main WHERE key = x'{ser_string(b'flags').hex()}'").fetchone()
+                new_flags = int.from_bytes(flags_rec[0], byteorder="little")
+                diff_flags = new_flags & ~old_flags
+
+                # Check for last hardened xpubs if the flag is newly set
+                if diff_flags & (1 << 2):
+                    self.log.debug("Checking descriptor cache was upgraded")
+                    # Fetch all records with the walletdescriptorlhcache prefix
+                    lh_cache_recs = conn.execute(f"SELECT value FROM main where key >= x'{ser_string(b'walletdescriptorlhcache').hex()}' AND key < x'{ser_string(b'walletdescriptorlhcachf').hex()}'").fetchall()
+                    assert_greater_than(len(lh_cache_recs), 0)
+
+            self.inspect_sqlite_db(down_backup_path, check_upgraded_records, old_flags)
+
             # Check that no automatic upgrade broke downgrading the wallet
             target_dir = node.wallets_path / down_wallet_name
             os.makedirs(target_dir, exist_ok=True)