merge bitcoin#22155: Add test for subtract fee from recipient behavior

src/Makefile.test.include

@@ -193,6 +193,7 @@ BITCOIN_TESTS += \
   wallet/test/bip39_tests.cpp \
   wallet/test/coinjoin_tests.cpp \
   wallet/test/psbt_wallet_tests.cpp \
+  wallet/test/spend_tests.cpp \
   wallet/test/wallet_tests.cpp \
   wallet/test/walletdb_tests.cpp \
   wallet/test/wallet_crypto_tests.cpp \
@@ -212,6 +213,8 @@ endif
 
 
 BITCOIN_TEST_SUITE += \
+  wallet/test/util.cpp \
+  wallet/test/util.h \
   wallet/test/wallet_test_fixture.cpp \
   wallet/test/wallet_test_fixture.h \
   wallet/test/init_test_fixture.cpp \

src/wallet/test/spend_tests.cpp

@@ -0,0 +1,61 @@
+// 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 <policy/fees.h>
+#include <validation.h>
+#include <wallet/coincontrol.h>
+#include <wallet/test/util.h>
+#include <wallet/test/wallet_test_fixture.h>
+
+#include <boost/test/unit_test.hpp>
+
+BOOST_FIXTURE_TEST_SUITE(spend_tests, WalletTestingSetup)
+
+BOOST_FIXTURE_TEST_CASE(SubtractFee, TestChain100Setup)
+{
+    CreateAndProcessBlock({}, GetScriptForRawPubKey(coinbaseKey.GetPubKey()));
+    auto wallet = CreateSyncedWallet(*m_node.chain, *m_node.coinjoin_loader, m_node.chainman->ActiveChain(), coinbaseKey);
+
+    // Check that a subtract-from-recipient transaction slightly less than the
+    // coinbase input amount does not create a change output (because it would
+    // be uneconomical to add and spend the output), and make sure it pays the
+    // leftover input amount which would have been change to the recipient
+    // instead of the miner.
+    auto check_tx = [&wallet](CAmount leftover_input_amount) {
+        CRecipient recipient{GetScriptForRawPubKey({}), 500 * COIN - leftover_input_amount, true /* subtract fee */};
+        CTransactionRef tx;
+        CAmount fee;
+        int change_pos = -1;
+        bilingual_str error;
+        CCoinControl coin_control;
+        coin_control.m_feerate.emplace(10000);
+        coin_control.fOverrideFeeRate = true;
+        FeeCalculation fee_calc;
+        BOOST_CHECK(wallet->CreateTransaction({recipient}, tx, fee, change_pos, error, coin_control, fee_calc));
+        BOOST_CHECK_EQUAL(tx->vout.size(), 1);
+        BOOST_CHECK_EQUAL(tx->vout[0].nValue, recipient.nAmount + leftover_input_amount - fee);
+        BOOST_CHECK_GT(fee, 0);
+        return fee;
+    };
+
+    // Send full input amount to recipient, check that only nonzero fee is
+    // subtracted (to_reduce == fee).
+    const CAmount fee{check_tx(0)};
+
+    // Send slightly less than full input amount to recipient, check leftover
+    // input amount is paid to recipient not the miner (to_reduce == fee - 123)
+    BOOST_CHECK_EQUAL(fee, check_tx(123));
+
+    // Send full input minus fee amount to recipient, check leftover input
+    // amount is paid to recipient not the miner (to_reduce == 0)
+    BOOST_CHECK_EQUAL(fee, check_tx(fee));
+
+    // Send full input minus more than the fee amount to recipient, check
+    // leftover input amount is paid to recipient not the miner (to_reduce ==
+    // -123). This overpays the recipient instead of overpaying the miner more
+    // than double the neccesary fee.
+    BOOST_CHECK_EQUAL(fee, check_tx(fee + 123));
+}
+
+BOOST_AUTO_TEST_SUITE_END()

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, interfaces::CoinJoin::Loader& coinjoin_loader, CChain& cchain, const CKey& key)
+{
+    auto wallet = std::make_unique<CWallet>(&chain, &coinjoin_loader, "", CreateMockWalletDatabase());
+    {
+        LOCK(wallet->cs_wallet);
+        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;
+}

src/wallet/test/util.h

@@ -0,0 +1,22 @@
+// 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.
+
+#ifndef BITCOIN_WALLET_TEST_UTIL_H
+#define BITCOIN_WALLET_TEST_UTIL_H
+
+#include <memory>
+
+class CChain;
+class CKey;
+class CWallet;
+namespace interfaces {
+class Chain;
+namespace CoinJoin {
+class Loader;
+} //namespsace CoinJoin
+} // namespace interfaces
+
+std::unique_ptr<CWallet> CreateSyncedWallet(interfaces::Chain& chain, interfaces::CoinJoin::Loader& coinjoin_loader, CChain& cchain, const CKey& key);
+
+#endif // BITCOIN_WALLET_TEST_UTIL_H

src/wallet/test/wallet_tests.cpp

@@ -26,6 +26,7 @@
 #include <policy/settings.h>
 #include <validation.h>
 #include <wallet/coincontrol.h>
+#include <wallet/test/util.h>
 #include <wallet/test/wallet_test_fixture.h>
 
 #include <boost/test/unit_test.hpp>
@@ -585,20 +586,7 @@ class ListCoinsTestingSetup : public TestChain100Setup
     ListCoinsTestingSetup()
     {
         CreateAndProcessBlock({}, GetScriptForRawPubKey(coinbaseKey.GetPubKey()));
-        wallet = std::make_unique<CWallet>(m_node.chain.get(), m_node.coinjoin_loader.get(), "", CreateMockWalletDatabase());
-        {
-            LOCK(wallet->cs_wallet);
-            wallet->SetLastBlockProcessed(m_node.chainman->ActiveChain().Height(), m_node.chainman->ActiveChain().Tip()->GetBlockHash());
-        }
-        wallet->LoadWallet();
-        AddKey(*wallet, coinbaseKey);
-        WalletRescanReserver reserver(*wallet);
-        reserver.reserve();
-        CWallet::ScanResult result = wallet->ScanForWalletTransactions(m_node.chainman->ActiveChain().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, m_node.chainman->ActiveChain().Tip()->GetBlockHash());
-        BOOST_CHECK_EQUAL(*result.last_scanned_height, m_node.chainman->ActiveChain().Height());
-        BOOST_CHECK(result.last_failed_block.IsNull());
+        wallet = CreateSyncedWallet(*m_node.chain, *m_node.coinjoin_loader, m_node.chainman->ActiveChain(), coinbaseKey);
     }
 
     ~ListCoinsTestingSetup()