test: wallet, fix change position out of range error

Since #25273, the behavior of 'inserting change at a random
position' is instructed by passing std::nullopt instead of -1.

Also, added missing documentation about the meaning of
'change_pos=std::nullopt' inside 'CWallet::CreateTransaction()'

2 files changed, 4 insertions, 4 deletions

diff --git a/src/wallet/test/spend_tests.cpp b/src/wallet/test/spend_tests.cpp
index b2d252b3f9..3509bc116f 100644
--- a/src/wallet/test/spend_tests.cpp
+++ b/src/wallet/test/spend_tests.cpp
@@ -33,7 +33,7 @@ BOOST_FIXTURE_TEST_CASE(SubtractFee, TestChain100Setup)
         coin_control.fOverrideFeeRate = true;
         // We need to use a change type with high cost of change so that the leftover amount will be dropped to fee instead of added as a change output
         coin_control.m_change_type = OutputType::LEGACY;
-        auto res = CreateTransaction(*wallet, {recipient}, std::nullopt, coin_control);
+        auto res = CreateTransaction(*wallet, {recipient}, /*change_pos=*/std::nullopt, coin_control);
         BOOST_CHECK(res);
         const auto& txr = *res;
         BOOST_CHECK_EQUAL(txr.tx->vout.size(), 1);
@@ -97,12 +97,12 @@ BOOST_FIXTURE_TEST_CASE(wallet_duplicated_preset_inputs_test, TestChain100Setup)
     // so that the recipient's amount is no longer equal to the user's selected target of 299 BTC.
 
     // First case, use 'subtract_fee_from_outputs=true'
-    util::Result<CreatedTransactionResult> res_tx = CreateTransaction(*wallet, recipients, /*change_pos*/-1, coin_control);
+    util::Result<CreatedTransactionResult> res_tx = CreateTransaction(*wallet, recipients, /*change_pos=*/std::nullopt, coin_control);
     BOOST_CHECK(!res_tx.has_value());
 
     // Second case, don't use 'subtract_fee_from_outputs'.
     recipients[0].fSubtractFeeFromAmount = false;
-    res_tx = CreateTransaction(*wallet, recipients, /*change_pos*/-1, coin_control);
+    res_tx = CreateTransaction(*wallet, recipients, /*change_pos=*/std::nullopt, coin_control);
     BOOST_CHECK(!res_tx.has_value());
 }
 
diff --git a/src/wallet/test/wallet_tests.cpp b/src/wallet/test/wallet_tests.cpp
index 3d1cbe36a8..1c5ca1483f 100644
--- a/src/wallet/test/wallet_tests.cpp
+++ b/src/wallet/test/wallet_tests.cpp
@@ -558,7 +558,7 @@ public:
         CTransactionRef tx;
         CCoinControl dummy;
         {
-            auto res = CreateTransaction(*wallet, {recipient}, std::nullopt, dummy);
+            auto res = CreateTransaction(*wallet, {recipient}, /*change_pos=*/std::nullopt, dummy);
             BOOST_CHECK(res);
             tx = res->tx;
         }