lsps2: Test payment lease state

Pin the direct lease serialization format and ensure fixed-amount and
variable-amount caches remain isolated. These focused checks complement
the end-to-end BOLT11 and BOLT12 coverage.

Co-Authored-By: HAL 9000

Author: tnull

src/liquidity/client/lsps2/state.rs

@@ -654,6 +654,33 @@ mod tests {
 		);
 	}
 
+	#[test]
+	fn payment_leases_roundtrip() {
+		let lease =
+			lease(2, 48, 100, Some(1_000), now_secs() + MIN_CACHED_LEASE_REMAINING_SECS + 60);
+
+		let encoded = lease.encode();
+		let decoded = PaymentLease::read(&mut &encoded[..]).unwrap();
+
+		assert_eq!(decoded, lease);
+	}
+
+	#[test]
+	fn fixed_and_variable_lease_pools_are_isolated() {
+		let valid_until = now_secs() + MIN_CACHED_LEASE_REMAINING_SECS + 60;
+		let fixed = lease(2, 49, 100, Some(1_000), valid_until);
+		let variable = lease(3, 50, 50, None, valid_until);
+		let available_lsps = [fixed.id.lsp_node_id, variable.id.lsp_node_id];
+		let mut state = LSPS2LeaseState::from_leases(vec![fixed.clone(), variable.clone()]);
+
+		let (selected_fixed, _) = state.fixed_amount(1_000, None, 1, &available_lsps).unwrap();
+		assert_eq!(selected_fixed.id, fixed.id);
+		assert!(state.fixed_amount(1_000, None, 1, &available_lsps).is_none());
+
+		let (selected_variable, _) = state.variable_amount(None, None, 1, &available_lsps).unwrap();
+		assert_eq!(selected_variable.id, variable.id);
+	}
+
 	#[test]
 	fn prunes_leases_close_to_expiry() {
 		let lease = lease(2, 43, 1, Some(1_000), now_secs() + MIN_CACHED_LEASE_REMAINING_SECS - 1);