test: add tests for LoadBlockIndex when using multiple chainstates

Incorporates feedback from Russ Yanofsky.

Author: jamesob

src/test/validation_chainstatemanager_tests.cpp

@@ -312,4 +312,81 @@ BOOST_FIXTURE_TEST_CASE(chainstatemanager_activate_snapshot, TestChain100Setup)
         loaded_snapshot_blockhash);
 }
 
+//! Test LoadBlockIndex behavior when multiple chainstates are in use.
+//!
+//! - First, verfiy that setBlockIndexCandidates is as expected when using a single,
+//!   fully-validating chainstate.
+//!
+//! - Then mark a region of the chain BLOCK_ASSUMED_VALID and introduce a second chainstate
+//!   that will tolerate assumed-valid blocks. Run LoadBlockIndex() and ensure that the first
+//!   chainstate only contains fully validated blocks and the other chainstate contains all blocks,
+//!   even those assumed-valid.
+//!
+BOOST_FIXTURE_TEST_CASE(chainstatemanager_loadblockindex, TestChain100Setup)
+{
+    ChainstateManager& chainman = *Assert(m_node.chainman);
+    CTxMemPool& mempool = *m_node.mempool;
+    CChainState& cs1 = chainman.ActiveChainstate();
+
+    int num_indexes{0};
+    int num_assumed_valid{0};
+    const int expected_assumed_valid{20};
+    const int last_assumed_valid_idx{40};
+    const int assumed_valid_start_idx = last_assumed_valid_idx - expected_assumed_valid;
+
+    CBlockIndex* validated_tip{nullptr};
+    CBlockIndex* assumed_tip{chainman.ActiveChain().Tip()};
+
+    auto reload_all_block_indexes = [&]() {
+        for (CChainState* cs : chainman.GetAll()) {
+            LOCK(::cs_main);
+            cs->UnloadBlockIndex();
+            BOOST_CHECK(cs->setBlockIndexCandidates.empty());
+        }
+
+        WITH_LOCK(::cs_main, chainman.LoadBlockIndex());
+    };
+
+    // Ensure that without any assumed-valid BlockIndex entries, all entries are considered
+    // tip candidates.
+    reload_all_block_indexes();
+    BOOST_CHECK_EQUAL(cs1.setBlockIndexCandidates.size(), cs1.m_chain.Height() + 1);
+
+    // Mark some region of the chain assumed-valid.
+    for (int i = 0; i <= cs1.m_chain.Height(); ++i) {
+        auto index = cs1.m_chain[i];
+
+        if (i < last_assumed_valid_idx && i >= assumed_valid_start_idx) {
+            index->nStatus = BlockStatus::BLOCK_VALID_TREE | BlockStatus::BLOCK_ASSUMED_VALID;
+        }
+
+        ++num_indexes;
+        if (index->IsAssumedValid()) ++num_assumed_valid;
+
+        // Note the last fully-validated block as the expected validated tip.
+        if (i == (assumed_valid_start_idx - 1)) {
+            validated_tip = index;
+            BOOST_CHECK(!index->IsAssumedValid());
+        }
+    }
+
+    BOOST_CHECK_EQUAL(expected_assumed_valid, num_assumed_valid);
+
+    CChainState& cs2 = WITH_LOCK(::cs_main,
+        return chainman.InitializeChainstate(&mempool, GetRandHash()));
+
+    reload_all_block_indexes();
+
+    // The fully validated chain only has candidates up to the start of the assumed-valid
+    // blocks.
+    BOOST_CHECK_EQUAL(cs1.setBlockIndexCandidates.count(validated_tip), 1);
+    BOOST_CHECK_EQUAL(cs1.setBlockIndexCandidates.count(assumed_tip), 0);
+    BOOST_CHECK_EQUAL(cs1.setBlockIndexCandidates.size(), assumed_valid_start_idx);
+
+    // The assumed-valid tolerant chain has all blocks as candidates.
+    BOOST_CHECK_EQUAL(cs2.setBlockIndexCandidates.count(validated_tip), 1);
+    BOOST_CHECK_EQUAL(cs2.setBlockIndexCandidates.count(assumed_tip), 1);
+    BOOST_CHECK_EQUAL(cs2.setBlockIndexCandidates.size(), num_indexes);
+}
+
 BOOST_AUTO_TEST_SUITE_END()