diff --git a/src/test/util/setup_common.h b/src/test/util/setup_common.h
--- a/src/test/util/setup_common.h
+++ b/src/test/util/setup_common.h
@@ -132,15 +132,16 @@
 class CMutableTransaction;
 class CScript;
 
-//
-// Testing fixture that pre-creates a
-// 100-block REGTEST-mode block chain
-//
+/**
+ * Testing fixture that pre-creates a 100-block REGTEST-mode block chain
+ */
 struct TestChain100Setup : public RegTestingSetup {
     TestChain100Setup();
 
-    // Create a new block with just given transactions, coinbase paying to
-    // scriptPubKey, and try to add it to the current chain.
+    /**
+     * Create a new block with just given transactions, coinbase paying to
+     * scriptPubKey, and try to add it to the current chain.
+     */
     CBlock CreateAndProcessBlock(const std::vector<CMutableTransaction> &txns,
                                  const CScript &scriptPubKey);
 
diff --git a/src/test/util/setup_common.cpp b/src/test/util/setup_common.cpp
--- a/src/test/util/setup_common.cpp
+++ b/src/test/util/setup_common.cpp
@@ -249,19 +249,14 @@
     }
 }
 
-//
-// Create a new block with just given transactions, coinbase paying to
-// scriptPubKey, and try to add it to the current chain.
-//
 CBlock TestChain100Setup::CreateAndProcessBlock(
     const std::vector<CMutableTransaction> &txns, const CScript &scriptPubKey) {
     const Config &config = GetConfig();
-    std::unique_ptr<CBlockTemplate> pblocktemplate =
-        BlockAssembler(config, *m_node.mempool).CreateNewBlock(scriptPubKey);
-    CBlock &block = pblocktemplate->block;
+    CTxMemPool empty_pool;
+    CBlock block =
+        BlockAssembler(config, empty_pool).CreateNewBlock(scriptPubKey)->block;
 
-    // Replace mempool-selected txns with just coinbase plus passed-in txns:
-    block.vtx.resize(1);
+    Assert(block.vtx.size() == 1);
     for (const CMutableTransaction &tx : txns) {
         block.vtx.push_back(MakeTransactionRef(tx));
     }
@@ -291,8 +286,7 @@
     Assert(m_node.chainman)
         ->ProcessNewBlock(config, shared_pblock, true, nullptr);
 
-    CBlock result = block;
-    return result;
+    return block;
 }
 
 TestChain100Setup::~TestChain100Setup() {}