Move peer eviction tests to a separate test file

out of net_tests, because the eviction tests:

- are a different domain of test coverage, with different dependencies

- run more slowly than the net tests

- will be growing in size, in this PR branch and in the future, as eviction
  test coverage is improved

1 files changed, 160 insertions, 0 deletions

diff --git a/src/test/net_peer_eviction_tests.cpp b/src/test/net_peer_eviction_tests.cpp
new file mode 100644
index 0000000000..b80beeac5a
--- /dev/null
+++ b/src/test/net_peer_eviction_tests.cpp
@@ -0,0 +1,160 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <net.h>
+#include <test/util/setup_common.h>
+
+#include <boost/test/unit_test.hpp>
+
+#include <algorithm>
+#include <functional>
+#include <optional>
+#include <vector>
+
+BOOST_FIXTURE_TEST_SUITE(net_peer_eviction_tests, BasicTestingSetup)
+
+std::vector<NodeEvictionCandidate> GetRandomNodeEvictionCandidates(const int n_candidates, FastRandomContext& random_context)
+{
+    std::vector<NodeEvictionCandidate> candidates;
+    for (int id = 0; id < n_candidates; ++id) {
+        candidates.push_back({
+            /* id */ id,
+            /* nTimeConnected */ static_cast<int64_t>(random_context.randrange(100)),
+            /* m_min_ping_time */ std::chrono::microseconds{random_context.randrange(100)},
+            /* nLastBlockTime */ static_cast<int64_t>(random_context.randrange(100)),
+            /* nLastTXTime */ static_cast<int64_t>(random_context.randrange(100)),
+            /* fRelevantServices */ random_context.randbool(),
+            /* fRelayTxes */ random_context.randbool(),
+            /* fBloomFilter */ random_context.randbool(),
+            /* nKeyedNetGroup */ random_context.randrange(100),
+            /* prefer_evict */ random_context.randbool(),
+            /* m_is_local */ random_context.randbool(),
+        });
+    }
+    return candidates;
+}
+
+// Returns true if any of the node ids in node_ids are selected for eviction.
+bool IsEvicted(std::vector<NodeEvictionCandidate> candidates, const std::vector<NodeId>& node_ids, FastRandomContext& random_context)
+{
+    Shuffle(candidates.begin(), candidates.end(), random_context);
+    const std::optional<NodeId> evicted_node_id = SelectNodeToEvict(std::move(candidates));
+    if (!evicted_node_id) {
+        return false;
+    }
+    return std::find(node_ids.begin(), node_ids.end(), *evicted_node_id) != node_ids.end();
+}
+
+// Create number_of_nodes random nodes, apply setup function candidate_setup_fn,
+// apply eviction logic and then return true if any of the node ids in node_ids
+// are selected for eviction.
+bool IsEvicted(const int number_of_nodes, std::function<void(NodeEvictionCandidate&)> candidate_setup_fn, const std::vector<NodeId>& node_ids, FastRandomContext& random_context)
+{
+    std::vector<NodeEvictionCandidate> candidates = GetRandomNodeEvictionCandidates(number_of_nodes, random_context);
+    for (NodeEvictionCandidate& candidate : candidates) {
+        candidate_setup_fn(candidate);
+    }
+    return IsEvicted(candidates, node_ids, random_context);
+}
+
+namespace {
+constexpr int NODE_EVICTION_TEST_ROUNDS{10};
+constexpr int NODE_EVICTION_TEST_UP_TO_N_NODES{200};
+} // namespace
+
+BOOST_AUTO_TEST_CASE(peer_eviction_test)
+{
+    FastRandomContext random_context{true};
+
+    for (int i = 0; i < NODE_EVICTION_TEST_ROUNDS; ++i) {
+        for (int number_of_nodes = 0; number_of_nodes < NODE_EVICTION_TEST_UP_TO_N_NODES; ++number_of_nodes) {
+            // Four nodes with the highest keyed netgroup values should be
+            // protected from eviction.
+            BOOST_CHECK(!IsEvicted(
+                number_of_nodes, [number_of_nodes](NodeEvictionCandidate& candidate) {
+                    candidate.nKeyedNetGroup = number_of_nodes - candidate.id;
+                },
+                {0, 1, 2, 3}, random_context));
+
+            // Eight nodes with the lowest minimum ping time should be protected
+            // from eviction.
+            BOOST_CHECK(!IsEvicted(
+                number_of_nodes, [](NodeEvictionCandidate& candidate) {
+                    candidate.m_min_ping_time = std::chrono::microseconds{candidate.id};
+                },
+                {0, 1, 2, 3, 4, 5, 6, 7}, random_context));
+
+            // Four nodes that most recently sent us novel transactions accepted
+            // into our mempool should be protected from eviction.
+            BOOST_CHECK(!IsEvicted(
+                number_of_nodes, [number_of_nodes](NodeEvictionCandidate& candidate) {
+                    candidate.nLastTXTime = number_of_nodes - candidate.id;
+                },
+                {0, 1, 2, 3}, random_context));
+
+            // Up to eight non-tx-relay peers that most recently sent us novel
+            // blocks should be protected from eviction.
+            BOOST_CHECK(!IsEvicted(
+                number_of_nodes, [number_of_nodes](NodeEvictionCandidate& candidate) {
+                    candidate.nLastBlockTime = number_of_nodes - candidate.id;
+                    if (candidate.id <= 7) {
+                        candidate.fRelayTxes = false;
+                        candidate.fRelevantServices = true;
+                    }
+                },
+                {0, 1, 2, 3, 4, 5, 6, 7}, random_context));
+
+            // Four peers that most recently sent us novel blocks should be
+            // protected from eviction.
+            BOOST_CHECK(!IsEvicted(
+                number_of_nodes, [number_of_nodes](NodeEvictionCandidate& candidate) {
+                    candidate.nLastBlockTime = number_of_nodes - candidate.id;
+                },
+                {0, 1, 2, 3}, random_context));
+
+            // Combination of the previous two tests.
+            BOOST_CHECK(!IsEvicted(
+                number_of_nodes, [number_of_nodes](NodeEvictionCandidate& candidate) {
+                    candidate.nLastBlockTime = number_of_nodes - candidate.id;
+                    if (candidate.id <= 7) {
+                        candidate.fRelayTxes = false;
+                        candidate.fRelevantServices = true;
+                    }
+                },
+                {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11}, random_context));
+
+            // Combination of all tests above.
+            BOOST_CHECK(!IsEvicted(
+                number_of_nodes, [number_of_nodes](NodeEvictionCandidate& candidate) {
+                    candidate.nKeyedNetGroup = number_of_nodes - candidate.id;           // 4 protected
+                    candidate.m_min_ping_time = std::chrono::microseconds{candidate.id}; // 8 protected
+                    candidate.nLastTXTime = number_of_nodes - candidate.id;              // 4 protected
+                    candidate.nLastBlockTime = number_of_nodes - candidate.id;           // 4 protected
+                },
+                {0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19}, random_context));
+
+            // An eviction is expected given >= 29 random eviction candidates. The eviction logic protects at most
+            // four peers by net group, eight by lowest ping time, four by last time of novel tx, up to eight non-tx-relay
+            // peers by last novel block time, and four more peers by last novel block time.
+            if (number_of_nodes >= 29) {
+                BOOST_CHECK(SelectNodeToEvict(GetRandomNodeEvictionCandidates(number_of_nodes, random_context)));
+            }
+
+            // No eviction is expected given <= 20 random eviction candidates. The eviction logic protects at least
+            // four peers by net group, eight by lowest ping time, four by last time of novel tx and four peers by last
+            // novel block time.
+            if (number_of_nodes <= 20) {
+                BOOST_CHECK(!SelectNodeToEvict(GetRandomNodeEvictionCandidates(number_of_nodes, random_context)));
+            }
+
+            // Cases left to test:
+            // * "Protect the half of the remaining nodes which have been connected the longest. [...]"
+            // * "Pick out up to 1/4 peers that are localhost, sorted by longest uptime. [...]"
+            // * "If any remaining peers are preferred for eviction consider only them. [...]"
+            // * "Identify the network group with the most connections and youngest member. [...]"
+        }
+    }
+}
+
+BOOST_AUTO_TEST_SUITE_END()