LibWeb+Tests: Demonstrate slowness of CSS::value_id_from_string

Author: https://github.com/BenWiederhake
Commit: https://github.com/SerenityOS/serenity/commit/b3d2fdceb1
Pull-request: https://github.com/SerenityOS/serenity/pull/16934
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/davidot

Tests/LibWeb/CMakeLists.txt

@@ -1,4 +1,5 @@
 set(TEST_SOURCES
+    TestCSSIDSpeed.cpp
     TestHTMLTokenizer.cpp
 )
 

Tests/LibWeb/TestCSSIDSpeed.cpp

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2023, Ben Wiederhake <BenWiederhake.GitHub@gmx.de>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibTest/TestCase.h>
+
+#include <LibWeb/CSS/ValueID.h>
+
+TEST_CASE(basic)
+{
+    EXPECT_EQ(Web::CSS::value_id_from_string("italic"sv), Web::CSS::ValueID::Italic);
+    EXPECT_EQ(Web::CSS::value_id_from_string("inline"sv), Web::CSS::ValueID::Inline);
+    EXPECT_EQ(Web::CSS::value_id_from_string("small"sv), Web::CSS::ValueID::Small);
+    EXPECT_EQ(Web::CSS::value_id_from_string("smalL"sv), Web::CSS::ValueID::Small);
+    EXPECT_EQ(Web::CSS::value_id_from_string("SMALL"sv), Web::CSS::ValueID::Small);
+    EXPECT_EQ(Web::CSS::value_id_from_string("Small"sv), Web::CSS::ValueID::Small);
+    EXPECT_EQ(Web::CSS::value_id_from_string("smALl"sv), Web::CSS::ValueID::Small);
+}
+
+BENCHMARK_CASE(value_id_from_string)
+{
+    for (size_t i = 0; i < 10'000'000; ++i) {
+        EXPECT_EQ(Web::CSS::value_id_from_string("inline"sv), Web::CSS::ValueID::Inline);
+    }
+}