Add proptest for future `last_seen` correction

Given a generated list of gossiped peers, ensure that after running the
`validate_addrs` function none of the resulting peers have a `last_seen`
time that's after the specified limit.

zebra-network/src/peer_set/candidate_set/tests.rs

@@ -1,3 +1,4 @@
 //! [`CandidateSet`] tests.
 
+mod prop;
 mod vectors;

zebra-network/src/peer_set/candidate_set/tests/prop.rs

@@ -0,0 +1,23 @@
+use proptest::{collection::vec, prelude::*};
+
+use zebra_chain::serialization::DateTime32;
+
+use super::super::validate_addrs;
+use crate::types::MetaAddr;
+
+proptest! {
+    /// Test that validated gossiped peers never have a `last_seen` time that's in the future.
+    #[test]
+    fn no_last_seen_times_are_in_the_future(
+        gossiped_peers in vec(MetaAddr::gossiped_strategy(), 1..10),
+        last_seen_limit in any::<DateTime32>(),
+    ) {
+        zebra_test::init();
+
+        let validated_peers = validate_addrs(gossiped_peers, last_seen_limit);
+
+        for peer in validated_peers {
+            prop_assert![peer.get_last_seen() <= last_seen_limit];
+        }
+    }
+}