From 3e6fd5705bc90f0d07cbd69f4700fe4be228bc53 Mon Sep 17 00:00:00 2001
From: Konstantin Osipov <kostja@scylladb.com>
Date: Fri, 16 Apr 2021 01:15:31 +0300
Subject: [PATCH] raft: (testing) test that non-voter stays in PIPELINE mode

Test that configuration changes preserve PIPELINE mode.
---
 test/raft/fsm_test.cc | 38 ++++++++++++++++++++++++++++++++++++++
 test/raft/helpers.hh  |  6 ++++++
 2 files changed, 44 insertions(+)

diff --git a/test/raft/fsm_test.cc b/test/raft/fsm_test.cc
index 0b8e24edfb..d25db45eb6 100644
--- a/test/raft/fsm_test.cc
+++ b/test/raft/fsm_test.cc
@@ -1549,3 +1549,41 @@ BOOST_AUTO_TEST_CASE(test_reordered_reject) {
     raft::logger.trace("delivering second reject");
     deliver(routes, fsm2.id(), std::move(reject_2.messages));
 }
+
+BOOST_AUTO_TEST_CASE(test_non_voter_stays_pipeline) {
+    // Check that a node stays in PIPELINE mode
+    // through configuration changes.
+    server_id A_id = id(), B_id = id();
+    raft::server_address_set addrset{raft::server_address{A_id}, raft::server_address{B_id, false}};
+    raft::configuration cfg(addrset);
+    raft::log log(raft::snapshot{.idx = index_t{0}, .config = cfg});
+    auto A = create_follower(A_id, log);
+    auto B = create_follower(B_id, log);
+    election_timeout(A);
+    communicate(A);
+    BOOST_CHECK(A.is_leader());
+    BOOST_CHECK(A.get_progress(B_id).state == raft::follower_progress::state::PROBE);
+    A.add_entry(log_entry::dummy{});
+    // We need to deliver a probe from A to B so that B gets
+    // a change to respond and A can switch B to PIPELINE mode.
+    A.tick();
+    communicate(A, B);
+    BOOST_CHECK(A.get_progress(B_id).state == raft::follower_progress::state::PIPELINE);
+    raft::configuration newcfg({A_id, B_id});
+    A.add_entry(newcfg);
+    communicate(A, B);
+    BOOST_CHECK_EQUAL(A.get_configuration().is_joint(), false);
+    BOOST_CHECK_EQUAL(A.get_configuration().current.find(raft::server_address{B_id})->can_vote, true);
+    BOOST_CHECK(A.get_progress(B_id).state == raft::follower_progress::state::PIPELINE);
+    A.add_entry(cfg);
+    auto tick_occasionally = [&A, &B]() {
+        if (rolladice()) {
+            A.tick(); B.tick();
+        }
+        return false;
+    };
+    communicate_until(tick_occasionally, A, B);
+    BOOST_CHECK_EQUAL(A.get_configuration().is_joint(), false);
+    BOOST_CHECK_EQUAL(A.get_configuration().current.find(raft::server_address{B_id})->can_vote, false);
+    BOOST_CHECK(A.get_progress(B_id).state == raft::follower_progress::state::PIPELINE);
+}
diff --git a/test/raft/helpers.hh b/test/raft/helpers.hh
index 51ca86b23a..a56d84973a 100644
--- a/test/raft/helpers.hh
+++ b/test/raft/helpers.hh
@@ -29,6 +29,7 @@
 
 #include <boost/test/unit_test.hpp>
 #include "test/lib/log.hh"
+#include "test/lib/random_utils.hh"
 #include "serializer_impl.hh"
 #include <limits>
 
@@ -241,3 +242,8 @@ raft::server_address to_server_address(size_t local_id) {
 size_t to_local_id(utils::UUID uuid) {
     return uuid.get_least_significant_bits() - 1;
 }
+
+// Return true upon a random event with given probability
+bool rolladice(float probability = 1.0/2.0) {
+    return tests::random::get_real(0.0, 1.0) < probability;
+}