Create the TestCaseTextIndexHelper.

LrcParser.Tests/Helper/TestCaseTextIndexHelper.cs

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+// Copyright (c) karaoke.dev <[email protected]>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System.Text.RegularExpressions;
+using LrcParser.Extension;
+using LrcParser.Model;
+
+namespace LrcParser.Tests.Helper;
+
+public static class TestCaseTextIndexHelper
+{
+    public static TextIndex ParseTextIndex(string str)
+    {
+        var regex = new Regex("(?<index>[-0-9]+),(?<state>start|end)");
+        var result = regex.Match(str);
+        if (!result.Success)
+            throw new RegexMatchTimeoutException(nameof(str));
+
+        int index = result.GetGroupValue<int>("index");
+        var state = result.GetGroupValue<string>("state") == "start" ? IndexState.Start : IndexState.End;
+
+        return new TextIndex(index, state);
+    }
+}