Tests: Add test for case-insensitive matching

Author: https://github.com/sin-ack
Commit: https://github.com/SerenityOS/serenity/commit/9a9e7f03f29
Pull-request: https://github.com/SerenityOS/serenity/pull/8086
Reviewed-by: https://github.com/MaxWipfli
Reviewed-by: https://github.com/alimpfard
Reviewed-by: https://github.com/gmta
Reviewed-by: https://github.com/gunnarbeutner

Tests/LibRegex/Regex.cpp

@@ -4,6 +4,7 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#include "LibRegex/RegexMatcher.h"
 #include <LibTest/TestCase.h> // import first, to prevent warning of VERIFY* redefinition
 
 #include <AK/StringBuilder.h>
@@ -595,3 +596,12 @@ TEST_CASE(replace)
         EXPECT_EQ(re.replace(test.subject, test.replacement), test.expected);
     }
 }
+
+TEST_CASE(case_insensitive_match)
+{
+    Regex<PosixExtended> re("cd", PosixFlags::Insensitive | PosixFlags::Global);
+    auto result = re.match("AEKFCD");
+
+    EXPECT_EQ(result.success, true);
+    EXPECT_EQ(result.matches.at(0).column, 4ul);
+}