Merge bitcoin#18195: test: Add cost_of_change parameter assertions to bnb_search_test

c72a11a test: Add cost_of_change parameter assertions to bnb_search_test (Yancy Ribbens)

Pull request description:

  If the `cost_of_change` variable is removed from the method body `SelectCoinsBnB`, there are currently no failing unit tests.  This PR adds assertions about the behavior of the `cost_of_change`:  If the cost of creating a change output is greater than what's leftover, then consume the output and create no change, otherwise, don't consume the output (no match found).

ACKs for top commit:
  achow101:
    ACK c72a11a

Tree-SHA512: 613aa411df5e2911446e0e8bf3309336faaadf2d3c56e7d125b76454e7c6f9e4f5e8f0910dc6222282628e38cd8a4a7c56bb3d36b564a17f396b9b503ecc64c8

Author: MarcoFalke

src/wallet/test/coinselector_tests.cpp

@@ -189,6 +189,19 @@ BOOST_AUTO_TEST_CASE(bnb_search_test)
     actual_selection.clear();
     selection.clear();
 
+    // Cost of change is greater than the difference between target value and utxo sum
+    add_coin(1 * CENT, 1, actual_selection);
+    BOOST_CHECK(SelectCoinsBnB(GroupCoins(utxo_pool), 0.9 * CENT, 0.5 * CENT, selection, value_ret, not_input_fees));
+    BOOST_CHECK_EQUAL(value_ret, 1 * CENT);
+    BOOST_CHECK(equal_sets(selection, actual_selection));
+    actual_selection.clear();
+    selection.clear();
+
+    // Cost of change is less than the difference between target value and utxo sum
+    BOOST_CHECK(!SelectCoinsBnB(GroupCoins(utxo_pool), 0.9 * CENT, 0, selection, value_ret, not_input_fees));
+    actual_selection.clear();
+    selection.clear();
+
     // Select 10 Cent
     add_coin(5 * CENT, 5, utxo_pool);
     add_coin(4 * CENT, 4, actual_selection);