tests: Add fuzzing harness for FeeFilterRounder

src/test/fuzz/fees.cpp

@@ -0,0 +1,26 @@
+// 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 <amount.h>
+#include <optional.h>
+#include <policy/fees.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.h>
+
+#include <cstdint>
+#include <string>
+#include <vector>
+
+void test_one_input(const std::vector<uint8_t>& buffer)
+{
+    FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
+    const CFeeRate minimal_incremental_fee{ConsumeMoney(fuzzed_data_provider)};
+    FeeFilterRounder fee_filter_rounder{minimal_incremental_fee};
+    while (fuzzed_data_provider.ConsumeBool()) {
+        const CAmount current_minimum_fee = ConsumeMoney(fuzzed_data_provider);
+        const CAmount rounded_fee = fee_filter_rounder.round(current_minimum_fee);
+        assert(MoneyRange(rounded_fee));
+    }
+}