test: Add some difficulty tests

test/unittests/CMakeLists.txt

@@ -34,6 +34,7 @@ target_sources(
     execution_state_test.cpp
     instructions_test.cpp
     state_bloom_filter_test.cpp
+    state_difficulty_test.cpp
     state_mpt_hash_test.cpp
     state_mpt_test.cpp
     state_new_account_address_test.cpp

test/unittests/state_difficulty_test.cpp

@@ -0,0 +1,75 @@
+// evmone: Fast Ethereum Virtual Machine implementation
+// Copyright 2023 The evmone Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+#include <gmock/gmock.h>
+#include <test/state/ethash_difficulty.hpp>
+
+using namespace evmone::state;
+
+struct DifficultyTest  // NOLINT(clang-analyzer-optin.performance.Padding)
+{
+    evmc_revision rev;
+    const char* name;
+    int64_t block_number;
+    int64_t difficulty;
+    int64_t timestamp;
+    int64_t parent_difficulty;
+    int64_t parent_timestamp;
+    bool parent_has_ommers;
+};
+
+/// Example difficulty tests from
+/// https://github.com/ethereum/tests/blob/develop/DifficultyTests.
+static constexpr DifficultyTest tests[] = {
+    {
+        EVMC_BYZANTIUM,
+        "DifficultyTest1",
+        0x0186a0,
+        0x69702c7f2c9fad14,
+        0x28d214819,
+        0x6963001f28ba95c2,
+        0x28d214818,
+        false,
+    },
+    {
+        EVMC_BYZANTIUM,
+        "DifficultyTest1038",
+        0x0dbba0,
+        0x79f2cbb8c97579b0,
+        0x72e440371,
+        0x79f2cbb8c97579b0,
+        0x72e44035d,
+        true,
+    },
+    {
+        EVMC_BERLIN,
+        "DifficultyTest1",
+        0x186a0,
+        0x56c67d1e106966c3,
+        0x63ed689e9,
+        0x56bba5a95b3dff04,
+        0x63ed689e8,
+        false,
+    },
+    {
+        EVMC_BERLIN,
+        "DifficultyTest1040",
+        0x10c8e0,
+        0x68f7512123928555,
+        0x617ec9fcc,
+        0x68f7512123928555,
+        0x617ec9fb8,
+        true,
+    },
+};
+
+TEST(state_difficulty, tests)
+{
+    for (const auto& t : tests)
+    {
+        const auto difficulty = calculate_difficulty(t.parent_difficulty, t.parent_has_ommers,
+            t.parent_timestamp, t.timestamp, t.block_number, t.rev);
+        EXPECT_EQ(difficulty, t.difficulty) << t.rev << "/" << t.name;
+    }
+}