tests: Add fuzzing harness for functions/classes in flatfile.h

src/test/fuzz/flatfile.cpp

@@ -0,0 +1,30 @@
+// 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 <flatfile.h>
+#include <optional.h>
+#include <test/fuzz/FuzzedDataProvider.h>
+#include <test/fuzz/fuzz.h>
+#include <test/fuzz/util.h>
+
+#include <cassert>
+#include <cstdint>
+#include <string>
+#include <vector>
+
+void test_one_input(const std::vector<uint8_t>& buffer)
+{
+    FuzzedDataProvider fuzzed_data_provider(buffer.data(), buffer.size());
+    Optional<FlatFilePos> flat_file_pos = ConsumeDeserializable<FlatFilePos>(fuzzed_data_provider);
+    if (!flat_file_pos) {
+        return;
+    }
+    Optional<FlatFilePos> another_flat_file_pos = ConsumeDeserializable<FlatFilePos>(fuzzed_data_provider);
+    if (another_flat_file_pos) {
+        assert((*flat_file_pos == *another_flat_file_pos) != (*flat_file_pos != *another_flat_file_pos));
+    }
+    (void)flat_file_pos->ToString();
+    flat_file_pos->SetNull();
+    assert(flat_file_pos->IsNull());
+}