tests: Use legacy change type in subtract fee from outputs test

The subtract fee from outputs assumes that the leftover input amount
will be dropped to fees. However this only happens if that amount is
less than the cost of change. In the event that it is higher than the
cost of change, the leftover amount will actually become a change
output. To avoid this scenario, force a change type which has a high
cost of change.

Author: achow101

src/wallet/test/spend_tests.cpp

@@ -33,6 +33,8 @@ BOOST_FIXTURE_TEST_CASE(SubtractFee, TestChain100Setup)
         CCoinControl coin_control;
         coin_control.m_feerate.emplace(10000);
         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;
         FeeCalculation fee_calc;
         BOOST_CHECK(CreateTransaction(*wallet, {recipient}, tx, fee, change_pos, error, coin_control, fee_calc));
         BOOST_CHECK_EQUAL(tx->vout.size(), 1);