Tests/LibCore: Add some basic AnonymousBuffer tests

Author: https://github.com/tcl3
Commit: https://github.com/LadybirdBrowser/ladybird/commit/1b5f85da1e4
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/9031
Reviewed-by: https://github.com/trflynn89 ✅

Tests/LibCore/CMakeLists.txt

@@ -1,4 +1,5 @@
 set(TEST_SOURCES
+    TestLibCoreAnonymousBuffer.cpp
     TestLibCoreArgsParser.cpp
     TestLibCoreDeferredInvoke.cpp
     TestLibCoreEventLoop.cpp

Tests/LibCore/TestLibCoreAnonymousBuffer.cpp

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2026, Tim Ledbetter <tim.ledbetter@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/ByteBuffer.h>
+#include <LibCore/AnonymousBuffer.h>
+#include <LibCore/System.h>
+#include <LibTest/TestCase.h>
+#include <string.h>
+
+TEST_CASE(create_with_size)
+{
+    auto buffer = MUST(Core::AnonymousBuffer::create_with_size(1024));
+    EXPECT(buffer.is_valid());
+    EXPECT_NE(buffer.fd(), -1);
+    EXPECT_EQ(buffer.size(), 1024u);
+    EXPECT_NE(buffer.data<void>(), nullptr);
+    EXPECT_EQ(buffer.bytes().size(), 1024u);
+}
+
+TEST_CASE(default_constructed_is_invalid)
+{
+    Core::AnonymousBuffer buffer;
+    EXPECT(!buffer.is_valid());
+    EXPECT_EQ(buffer.fd(), -1);
+    EXPECT_EQ(buffer.size(), 0u);
+    EXPECT_EQ(buffer.data<void>(), nullptr);
+    EXPECT(buffer.bytes().is_empty());
+}
+
+TEST_CASE(read_and_write_contents)
+{
+    auto buffer = MUST(Core::AnonymousBuffer::create_with_size(64));
+
+    auto const payload = "hello, anonymous buffer!"sv;
+    memcpy(buffer.data<void>(), payload.characters_without_null_termination(), payload.length());
+
+    auto const* data = buffer.data<char const>();
+    StringView read_back { data, payload.length() };
+    EXPECT_EQ(read_back, payload);
+}
+
+TEST_CASE(reconstruct_from_anon_fd_shares_memory)
+{
+    auto original = MUST(Core::AnonymousBuffer::create_with_size(128));
+
+    auto const payload = "shared across mappings"sv;
+    memcpy(original.data<void>(), payload.characters_without_null_termination(), payload.length());
+
+    auto fd = MUST(Core::System::dup(original.fd()));
+    auto mirror = MUST(Core::AnonymousBuffer::create_from_anon_fd(fd, original.size()));
+
+    EXPECT(mirror.is_valid());
+    EXPECT_EQ(mirror.size(), original.size());
+
+    StringView mirrored { mirror.data<char const>(), payload.length() };
+    EXPECT_EQ(mirrored, payload);
+}