wallet test refactor: add CreateSyncedWallet function

No change in behavior. This just moves some code from the ListCoins test
setup to a reusable util function, so it can be reused in a new test in
the next commit.

src/wallet/test/util.cpp

@@ -0,0 +1,38 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <wallet/test/util.h>
+
+#include <chain.h>
+#include <key.h>
+#include <test/util/setup_common.h>
+#include <wallet/wallet.h>
+#include <wallet/walletdb.h>
+
+#include <boost/test/unit_test.hpp>
+
+#include <memory>
+
+std::unique_ptr<CWallet> CreateSyncedWallet(interfaces::Chain& chain, CChain& cchain, const CKey& key)
+{
+    auto wallet = std::make_unique<CWallet>(&chain, "", CreateMockWalletDatabase());
+    {
+        LOCK2(wallet->cs_wallet, ::cs_main);
+        wallet->SetLastBlockProcessed(cchain.Height(), cchain.Tip()->GetBlockHash());
+    }
+    wallet->LoadWallet();
+    {
+        auto spk_man = wallet->GetOrCreateLegacyScriptPubKeyMan();
+        LOCK2(wallet->cs_wallet, spk_man->cs_KeyStore);
+        spk_man->AddKeyPubKey(key, key.GetPubKey());
+    }
+    WalletRescanReserver reserver(*wallet);
+    reserver.reserve();
+    CWallet::ScanResult result = wallet->ScanForWalletTransactions(cchain.Genesis()->GetBlockHash(), 0 /* start_height */, {} /* max_height */, reserver, false /* update */);
+    BOOST_CHECK_EQUAL(result.status, CWallet::ScanResult::SUCCESS);
+    BOOST_CHECK_EQUAL(result.last_scanned_block, cchain.Tip()->GetBlockHash());
+    BOOST_CHECK_EQUAL(*result.last_scanned_height, cchain.Height());
+    BOOST_CHECK(result.last_failed_block.IsNull());
+    return wallet;
+}