Merge bitcoin/bitcoin#23132: test: Change background_cs from pointer to reference in validation_chainstate_tests

fa4d0aa test: * -> & (MarcoFalke)

Pull request description:

  This changes background_cs from being a pointer to a reference to work
  around a gcc false warning. Also, this makes the test easier to read.

  Fixes bitcoin#23101

  Can be reviewed with --ignore-all-space.

ACKs for top commit:
  practicalswift:
    cr ACK fa4d0aa
  jamesob:
    ACK bitcoin/bitcoin@fa4d0aa
  hebasto:
    ACK fa4d0aa, tested on Linux Mint 20.2 (x86_64) by merging this PR on top of the current master.

Tree-SHA512: 93a0d8859201f7074bea52fab8f6701409148bc50cfbb142cacfa6c991fc12c07584df04fead645f11703883df99535423d154f9945202e1c5aff49540d9b607

Author: MarcoFalke

src/test/validation_chainstate_tests.cpp

@@ -107,20 +107,21 @@ BOOST_FIXTURE_TEST_CASE(chainstate_update_tip, TestChain100Setup)
 
     curr_tip = ::g_best_block;
 
-    CChainState* background_cs;
-
     BOOST_CHECK_EQUAL(chainman.GetAll().size(), 2);
-    for (CChainState* cs : chainman.GetAll()) {
-        if (cs != &chainman.ActiveChainstate()) {
-            background_cs = cs;
+
+    CChainState& background_cs{*[&] {
+        for (CChainState* cs : chainman.GetAll()) {
+            if (cs != &chainman.ActiveChainstate()) {
+                return cs;
+            }
         }
-    }
-    BOOST_CHECK(background_cs);
+        assert(false);
+    }()};
 
     // Create a block to append to the validation chain.
     std::vector<CMutableTransaction> noTxns;
     CScript scriptPubKey = CScript() << ToByteVector(coinbaseKey.GetPubKey()) << OP_CHECKSIG;
-    CBlock validation_block = this->CreateBlock(noTxns, scriptPubKey, *background_cs);
+    CBlock validation_block = this->CreateBlock(noTxns, scriptPubKey, background_cs);
     auto pblock = std::make_shared<const CBlock>(validation_block);
     BlockValidationState state;
     CBlockIndex* pindex = nullptr;
@@ -133,15 +134,15 @@ BOOST_FIXTURE_TEST_CASE(chainstate_update_tip, TestChain100Setup)
         LOCK(::cs_main);
         bool checked = CheckBlock(*pblock, state, chainparams.GetConsensus());
         BOOST_CHECK(checked);
-        bool accepted = background_cs->AcceptBlock(
+        bool accepted = background_cs.AcceptBlock(
             pblock, state, &pindex, true, nullptr, &newblock);
         BOOST_CHECK(accepted);
     }
     // UpdateTip is called here
-    bool block_added = background_cs->ActivateBestChain(state, pblock);
+    bool block_added = background_cs.ActivateBestChain(state, pblock);
 
     // Ensure tip is as expected
-    BOOST_CHECK_EQUAL(background_cs->m_chain.Tip()->GetBlockHash(), validation_block.GetHash());
+    BOOST_CHECK_EQUAL(background_cs.m_chain.Tip()->GetBlockHash(), validation_block.GetHash());
 
     // g_best_block should be unchanged after adding a block to the background
     // validation chain.