From aa87aae14f9eee79e3a0fb9c0f5ff3eaa97433e2 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C5=91rinc?= <pap.lorinc@gmail.com>
Date: Sat, 31 Jan 2026 21:02:19 +0100
Subject: [PATCH] consensus/test: add `MoneyRange` unit tests for
 `CheckTxInputs`

Add minimal unit tests exercising `Consensus::CheckTxInputs` reject reasons for coinbase maturity (`bad-txns-premature-spend-of-coinbase`), input value range failures (`bad-txns-inputvalues-outofrange`), and for `nValueIn < value_out` (`bad-txns-in-belowout`).

Inspired by b-c-cov coverage reports:
* "bad-txns-premature-spend-of-coinbase" - https://maflcko.github.io/b-c-cov/test_bitcoin.coverage/src/consensus/tx_verify.cpp.gcov.html#L180
* "bad-txns-inputvalues-outofrange" - https://maflcko.github.io/b-c-cov/test_bitcoin.coverage/src/consensus/tx_verify.cpp.gcov.html#L187
* "bad-txns-in-belowout" - https://maflcko.github.io/b-c-cov/test_bitcoin.coverage/src/consensus/tx_verify.cpp.gcov.html#L193
---
 src/test/transaction_tests.cpp | 41 ++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/src/test/transaction_tests.cpp b/src/test/transaction_tests.cpp
index 3919f226d69..0f175c7d6f3 100644
--- a/src/test/transaction_tests.cpp
+++ b/src/test/transaction_tests.cpp
@@ -9,6 +9,7 @@
 #include <checkqueue.h>
 #include <clientversion.h>
 #include <consensus/amount.h>
+#include <consensus/consensus.h>
 #include <consensus/tx_check.h>
 #include <consensus/tx_verify.h>
 #include <consensus/validation.h>
@@ -1114,6 +1115,46 @@ BOOST_AUTO_TEST_CASE(max_standard_legacy_sigops)
     BOOST_CHECK(!::AreInputsStandard(CTransaction(tx_max_sigops), coins));
 }
 
+BOOST_AUTO_TEST_CASE(checktxinputs_invalid_transactions_test)
+{
+    auto check_invalid{[](CAmount input_value, CAmount output_value, bool coinbase, int spend_height, TxValidationResult expected_result, std::string_view expected_reason) {
+        CCoinsView coins_dummy;
+        CCoinsViewCache inputs(&coins_dummy);
+
+        const COutPoint prevout{Txid::FromUint256(uint256::ONE), 0};
+        inputs.AddCoin(prevout, Coin{{input_value, CScript() << OP_TRUE}, /*nHeightIn=*/1, coinbase}, /*possible_overwrite=*/false);
+
+        CMutableTransaction mtx;
+        mtx.vin.emplace_back(prevout);
+        mtx.vout.emplace_back(output_value, CScript() << OP_TRUE);
+
+        TxValidationState state;
+        CAmount txfee{0};
+        BOOST_CHECK(!Consensus::CheckTxInputs(CTransaction{mtx}, state, inputs, spend_height, txfee));
+        BOOST_CHECK(state.IsInvalid());
+        BOOST_CHECK_EQUAL(state.GetResult(), expected_result);
+        BOOST_CHECK_EQUAL(state.GetRejectReason(), expected_reason);
+    }};
+
+    check_invalid(/*input_value=*/MAX_MONEY + 1,
+                  /*output_value=*/0,
+                  /*coinbase=*/false,
+                  /*spend_height=*/2,
+                  TxValidationResult::TX_CONSENSUS, /*expected_reason=*/"bad-txns-inputvalues-outofrange");
+
+    check_invalid(/*input_value=*/1 * COIN,
+                  /*output_value=*/2 * COIN,
+                  /*coinbase=*/false,
+                  /*spend_height=*/2,
+                  TxValidationResult::TX_CONSENSUS, /*expected_reason=*/"bad-txns-in-belowout");
+
+    check_invalid(/*input_value=*/1 * COIN,
+                  /*output_value=*/0,
+                  /*coinbase=*/true,
+                  /*spend_height=*/COINBASE_MATURITY,
+                  TxValidationResult::TX_PREMATURE_SPEND, /*expected_reason=*/"bad-txns-premature-spend-of-coinbase");
+}
+
 /** Sanity check the return value of SpendsNonAnchorWitnessProg for various output types. */
 BOOST_AUTO_TEST_CASE(spends_witness_prog)
 {