chore: add unit test

stackslib/src/net/inv/epoch2x.rs

@@ -1753,7 +1753,7 @@ impl PeerNetwork {
     }
 
     /// Determine at which reward cycle to begin scanning inventories
-    fn get_block_scan_start(&self, sortdb: &SortitionDB) -> u64 {
+    pub(crate) fn get_block_scan_start(&self, sortdb: &SortitionDB) -> u64 {
         // see if the stacks tip affirmation map and heaviest affirmation map diverge.  If so, then
         // start scaning at the reward cycle just before that.
         let am_rescan_rc = self
@@ -1786,10 +1786,12 @@ impl PeerNetwork {
         let rescan_rc = cmp::min(am_rescan_rc, start_reward_cycle);
 
         test_debug!(
-            "begin blocks inv scan at {} = min({},{})",
+            "begin blocks inv scan at {} = min({},{}) stacks_tip_am={} heaviest_am={}",
             rescan_rc,
-            stacks_tip_rc,
-            am_rescan_rc
+            am_rescan_rc,
+            start_reward_cycle,
+            &self.stacks_tip_affirmation_map,
+            &self.heaviest_affirmation_map
         );
         rescan_rc
     }

stackslib/src/net/tests/inv/epoch2x.rs

@@ -1241,6 +1241,56 @@ fn test_sync_inv_diagnose_nack() {
     );
 }
 
+#[test]
+fn test_inv_sync_start_reward_cycle() {
+    let mut peer_1_config = TestPeerConfig::new(function_name!(), 0, 0);
+    peer_1_config.connection_opts.inv_reward_cycles = 0;
+
+    let mut peer_1 = TestPeer::new(peer_1_config);
+
+    let num_blocks = (GETPOXINV_MAX_BITLEN * 2) as u64;
+    for i in 0..num_blocks {
+        let (burn_ops, stacks_block, microblocks) = peer_1.make_default_tenure();
+        peer_1.next_burnchain_block(burn_ops.clone());
+        peer_1.process_stacks_epoch_at_tip(&stacks_block, &microblocks);
+    }
+
+    let _ = peer_1.step();
+
+    let block_scan_start = peer_1
+        .network
+        .get_block_scan_start(peer_1.sortdb.as_ref().unwrap());
+    assert_eq!(block_scan_start, 7);
+
+    peer_1.network.connection_opts.inv_reward_cycles = 1;
+
+    let block_scan_start = peer_1
+        .network
+        .get_block_scan_start(peer_1.sortdb.as_ref().unwrap());
+    assert_eq!(block_scan_start, 7);
+
+    peer_1.network.connection_opts.inv_reward_cycles = 2;
+
+    let block_scan_start = peer_1
+        .network
+        .get_block_scan_start(peer_1.sortdb.as_ref().unwrap());
+    assert_eq!(block_scan_start, 6);
+
+    peer_1.network.connection_opts.inv_reward_cycles = 3;
+
+    let block_scan_start = peer_1
+        .network
+        .get_block_scan_start(peer_1.sortdb.as_ref().unwrap());
+    assert_eq!(block_scan_start, 5);
+
+    peer_1.network.connection_opts.inv_reward_cycles = 300;
+
+    let block_scan_start = peer_1
+        .network
+        .get_block_scan_start(peer_1.sortdb.as_ref().unwrap());
+    assert_eq!(block_scan_start, 0);
+}
+
 #[test]
 #[ignore]
 fn test_sync_inv_2_peers_plain() {