feat: Cache FetchLedgerBySeq (#2014)

fixes #1758

tests/unit/data/cassandra/LedgerHeaderCacheTests.cpp

@@ -0,0 +1,70 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2025, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include "data/LedgerHeaderCache.hpp"
+#include "util/TestObject.hpp"
+
+#include <gtest/gtest.h>
+#include <xrpl/basics/base_uint.h>
+#include <xrpl/protocol/LedgerHeader.h>
+
+using namespace data;
+using Test = ::testing::Test;
+
+constexpr auto kLEDGER_HASH = "4BC50C9B0D8515D3EAAE1E74B29A95804346C491EE1A95BF25E4AAB854A6A652";
+constinit auto const kLEDGER_HASH2 = "1B8590C01B0006EDFA9ED60296DD052DC5E90F99659B25014D08E1BC983515BC";
+
+class FetchLedgerCacheTest : public Test {
+protected:
+    FetchLedgerCache cache_;
+};
+
+TEST_F(FetchLedgerCacheTest, DefaultCacheIsEmpty)
+{
+    auto const result = cache_.get();
+    EXPECT_FALSE(result.has_value());
+}
+
+TEST_F(FetchLedgerCacheTest, CanStoreAndRetrieveEntry)
+{
+    auto const ledger = createLedgerHeader(kLEDGER_HASH, 42);
+    FetchLedgerCache::CacheEntry entry{.ledger = ledger, .seq = 42};
+
+    cache_.put(entry);
+    auto const result = cache_.get();
+
+    ASSERT_TRUE(result.has_value());
+    EXPECT_EQ(result.value(), entry);
+}
+
+TEST_F(FetchLedgerCacheTest, PutOverwritesPreviousEntry)
+{
+    auto const ledger1 = createLedgerHeader(kLEDGER_HASH, 1);
+    auto const ledger2 = createLedgerHeader(kLEDGER_HASH2, 2);
+
+    FetchLedgerCache::CacheEntry entry1{.ledger = ledger1, .seq = 1};
+    FetchLedgerCache::CacheEntry entry2{.ledger = ledger2, .seq = 2};
+
+    cache_.put(entry1);
+    cache_.put(entry2);
+
+    auto const result = cache_.get();
+    ASSERT_TRUE(result.has_value());
+    EXPECT_EQ(result.value(), entry2);
+}