Added failing test for tuple BnB metric ordering propagation

Author: EliteCoder18

tests/bnb.rs

@@ -52,6 +52,36 @@ impl BnbMetric for MinExcessThenWeight {
     }
 }
 
+#[derive(Clone, Copy)]
+struct OrderSensitive;
+
+impl BnbMetric for OrderSensitive {
+    fn score(&mut self, _cs: &CoinSelector<'_>) -> Option<Ordf32> {
+        Some(Ordf32(0.0))
+    }
+
+    fn bound(&mut self, _cs: &CoinSelector<'_>) -> Option<Ordf32> {
+        Some(Ordf32(0.0))
+    }
+
+    fn requires_ordering_by_descending_value_pwu(&self) -> bool {
+        true
+    }
+}
+
+#[derive(Clone, Copy)]
+struct NoOrderMetric;
+
+impl BnbMetric for NoOrderMetric {
+    fn score(&mut self, _cs: &CoinSelector<'_>) -> Option<Ordf32> {
+        Some(Ordf32(0.0))
+    }
+
+    fn bound(&mut self, _cs: &CoinSelector<'_>) -> Option<Ordf32> {
+        Some(Ordf32(0.0))
+    }
+}
+
 #[test]
 /// Detect regressions/improvements by making sure it always finds the solution in the same
 /// number of iterations.
@@ -139,6 +169,24 @@ fn bnb_finds_solution_if_possible_in_n_iter() {
     assert_eq!(excess, 0);
 }
 
+#[test]
+fn bnb_tuple_metric_respects_ordering_requirement() {
+    assert!(
+        ((OrderSensitive, 1.0), (OrderSensitive, 1.0)).requires_ordering_by_descending_value_pwu(),
+        "both require ordering, so ordering should be required"
+    );
+
+    assert!(
+        ((OrderSensitive, 1.0), (NoOrderMetric, 1.0)).requires_ordering_by_descending_value_pwu(),
+        "one requires ordering, so ordering should be required"
+    );
+
+    assert!(
+        !((NoOrderMetric, 1.0), (NoOrderMetric, 1.0)).requires_ordering_by_descending_value_pwu(),
+        "none require ordering, so ordering should not be required"
+    );
+}
+
 proptest! {
     #[test]
     fn bnb_always_finds_solution_if_possible(num_inputs in 1usize..18, target_value in 0u64..10_000) {