fuzz: Add MuHash consistency fuzz test

src/Makefile.test.include

@@ -229,6 +229,7 @@ test_fuzz_fuzz_SOURCES = \
  test/fuzz/locale.cpp \
  test/fuzz/merkleblock.cpp \
  test/fuzz/message.cpp \
+ test/fuzz/muhash.cpp \
  test/fuzz/multiplication_overflow.cpp \
  test/fuzz/net.cpp \
  test/fuzz/net_permissions.cpp \

src/test/fuzz/muhash.cpp

@@ -0,0 +1,53 @@
+// Copyright (c) 2020 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 <crypto/muhash.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.h>
+
+#include <vector>
+
+void test_one_input(const std::vector<uint8_t>& buffer)
+{
+    FuzzedDataProvider fuzzed_data_provider{buffer.data(), buffer.size()};
+    std::vector<uint8_t> data = ConsumeRandomLengthByteVector(fuzzed_data_provider);
+    std::vector<uint8_t> data2 = ConsumeRandomLengthByteVector(fuzzed_data_provider);
+    if (data.empty()) {
+        data.resize(fuzzed_data_provider.ConsumeIntegralInRange<size_t>(1, 4096), fuzzed_data_provider.ConsumeIntegral<uint8_t>());
+    }
+    if (data2.empty()) {
+        data2.resize(fuzzed_data_provider.ConsumeIntegralInRange<size_t>(1, 4096), fuzzed_data_provider.ConsumeIntegral<uint8_t>());
+    }
+
+    data = ConsumeRandomLengthByteVector(fuzzed_data_provider);
+    data2 = ConsumeRandomLengthByteVector(fuzzed_data_provider);
+
+    MuHash3072 muhash;
+
+    // Test that MuHash result is consistent independent of order of operations
+    muhash.Insert(data);
+    muhash.Insert(data2);
+
+    uint256 out;
+    muhash.Finalize(out);
+
+    muhash = MuHash3072();
+    muhash.Insert(data2);
+    muhash.Insert(data);
+
+    uint256 out2;
+    muhash.Finalize(out2);
+
+    assert(out == out2);
+
+    // Test that removing all added elements brings the object back to it's initial state
+    muhash /= muhash;
+    muhash.Finalize(out);
+
+    MuHash3072 muhash2;
+    muhash2.Finalize(out2);
+
+    assert(out == out2);
+}