test: adjust ComputeMerkleRoot tests

Update the integer fuzz test to move the vector into `ComputeMerkleRoot`, matching production usage patterns and avoiding unnecessary copies.

Update `merkle_test_BlockWitness` to use an odd number of transactions to ensure the test covers the scenario where leaf duplication occurs. Also switch to `GetWitnessHash` to match `BlockWitnessMerkleRoot` semantics.
The manual vector setup retains the exact-size `resize` to explicitly verify the behavior against the calculated root.

src/test/fuzz/integer.cpp

@@ -80,8 +80,8 @@ FUZZ_TARGET(integer, .init = initialize_integer)
     }
     constexpr uint256 u256_min{"0000000000000000000000000000000000000000000000000000000000000000"};
     constexpr uint256 u256_max{"ffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff"};
-    const std::vector<uint256> v256{u256, u256_min, u256_max};
-    (void)ComputeMerkleRoot(v256);
+    std::vector v256{u256, u256_min, u256_max};
+    (void)ComputeMerkleRoot(std::move(v256));
     (void)DecompressAmount(u64);
     {
         if (std::optional<CAmount> parsed = ParseMoney(FormatMoney(i64))) {

src/test/merkle_tests.cpp

@@ -232,8 +232,9 @@ BOOST_AUTO_TEST_CASE(merkle_test_BlockWitness)
 {
     CBlock block;
 
-    block.vtx.resize(2);
-    for (std::size_t pos = 0; pos < block.vtx.size(); pos++) {
+    constexpr size_t vtx_count{3};
+    block.vtx.resize(vtx_count);
+    for (std::size_t pos = 0; pos < vtx_count; pos++) {
         CMutableTransaction mtx;
         mtx.nLockTime = pos;
         block.vtx[pos] = MakeTransactionRef(std::move(mtx));
@@ -242,12 +243,12 @@ BOOST_AUTO_TEST_CASE(merkle_test_BlockWitness)
     uint256 blockWitness = BlockWitnessMerkleRoot(block);
 
     std::vector<uint256> hashes;
-    hashes.resize(block.vtx.size());
-    hashes[0].SetNull();
-    hashes[1] = block.vtx[1]->GetHash().ToUint256();
+    hashes.resize(vtx_count); // Note: leaving odd count to exercise old behavior
+    for (size_t pos{1}; pos < vtx_count; ++pos) {
+        hashes[pos] = block.vtx[pos]->GetWitnessHash().ToUint256();
+    }
 
     uint256 merkleRootofHashes = ComputeMerkleRoot(hashes);
-
     BOOST_CHECK_EQUAL(merkleRootofHashes, blockWitness);
 }
 BOOST_AUTO_TEST_SUITE_END()