test: check MIN_PEER_PROTO_VERSION peers are not disconnected #36522

Kills mutant https://bitcoincore.space/src/net_processing.cpp#3442

diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 61b8a4ecd8..73c91a5bd6 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -3647,7 +3647,7 @@ void PeerManagerImpl::ProcessMessage(Peer& peer, CNode& pfrom, const std::string
             return;
         }
 
-        if (nVersion < MIN_PEER_PROTO_VERSION) {
+        if (nVersion <= MIN_PEER_PROTO_VERSION) {
             // disconnect from peers older than this proto version
             LogDebug(BCLog::NET, "peer using obsolete version %i, %s", nVersion, pfrom.DisconnectMsg());
             pfrom.fDisconnect = true;

<!--e57a25ab6845829454e8d69fc972939a-->

The following sections might be updated with supplementary metadata relevant to reviewers and maintainers.

<!--006a51241073e994b41acfe9ec718e94-->

External sites

• Code coverage & benchmarks: https://corecheck.dev/bitcoin/bitcoin/pulls/36522
• Ralph review <img src=https://review.fish.foo/assets/bitcoin/bitcoin/36522.png alt="Ralph review status"> https://git.fish.foo/bitcoin/bitcoin/pulls/36522#author-ralph

<!--021abf342d371248e50ceaed478a90ca-->

Reviews

See the guideline and AI policy for information on the review process.

If your review is incorrectly listed, please copy-paste <code>&lt;!--meta-tag:bot-skip--&gt;</code> into the comment that the bot should ignore.

<!--5faf32d7da4f0f540f40219e4f7537a3-->

lgtm ACK 5b07c48b8387f387530a90ce5b4a1224b6703aa3

For reference, in case the third-party site goes down, the mutant diff was:

diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 61b8a4ecd8..73c91a5bd6 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -3647,7 +3647,7 @@ void PeerManagerImpl::ProcessMessage(Peer& peer, CNode& pfrom, const std::string
             return;
         }
 
-        if (nVersion < MIN_PEER_PROTO_VERSION) {
+        if (nVersion <= MIN_PEER_PROTO_VERSION) {
             // disconnect from peers older than this proto version
             LogDebug(BCLog::NET, "peer using obsolete version %i, %s", nVersion, pfrom.DisconnectMsg());
             pfrom.fDisconnect = true;

@maflcko copied into OP thanks

ACK 5b07c48b8387f387530a90ce5b4a1224b6703aa3

Verified it kills the mutant - see: https://mutanthub.space/mutants/1028

Please, check https://mutanthub.space/projects/bitcoin/bitcoin instead of https://bitcoincore.space next time (I’m going to disable it in favor of MutantHub).