test: add baseline tests for StringExtensions performance methods

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Co-Authored-By: Claude <noreply@anthropic.com>

tests/Umbraco.Tests.UnitTests/Umbraco.Core/Extensions/StringExtensionsPerformanceTests.cs

@@ -0,0 +1,54 @@
+// Copyright (c) Umbraco.
+// See LICENSE for more details.
+
+using NUnit.Framework;
+using Umbraco.Extensions;
+
+namespace Umbraco.Cms.Tests.UnitTests.Umbraco.Core.Extensions;
+
+[TestFixture]
+public class StringExtensionsPerformanceTests
+{
+    [TestCase("hello world", "helloworld")]
+    [TestCase("  spaces  everywhere  ", "spaceseverywhere")]
+    [TestCase("tabs\there", "tabshere")]
+    [TestCase("new\nlines", "newlines")]
+    public void StripWhitespace_RemovesAllWhitespace(string input, string expected)
+        => Assert.AreEqual(expected, input.StripWhitespace());
+
+    [TestCase("file.txt", ".txt")]
+    [TestCase("path/to/file.png", ".png")]
+    [TestCase("file.tar.gz", ".gz")]
+    [TestCase("noextension", "")]
+    public void GetFileExtension_ReturnsCorrectExtension(string input, string expected)
+        => Assert.AreEqual(expected, input.GetFileExtension());
+
+    [TestCase("<p>Hello</p>", "Hello")]
+    [TestCase("<div><span>Text</span></div>", "Text")]
+    [TestCase("No tags here", "No tags here")]
+    [TestCase("<br/>", "")]
+    public void StripHtml_RemovesAllHtmlTags(string input, string expected)
+        => Assert.AreEqual(expected, input.StripHtml());
+
+    [TestCase('a', true)]
+    [TestCase('z', true)]
+    [TestCase('A', false)]
+    [TestCase('Z', false)]
+    [TestCase('5', true)]
+    public void IsLowerCase_ReturnsCorrectResult(char input, bool expected)
+        => Assert.AreEqual(expected, input.IsLowerCase());
+
+    [TestCase('A', true)]
+    [TestCase('Z', true)]
+    [TestCase('a', false)]
+    [TestCase('z', false)]
+    [TestCase('5', true)]
+    public void IsUpperCase_ReturnsCorrectResult(char input, bool expected)
+        => Assert.AreEqual(expected, input.IsUpperCase());
+
+    [TestCase("hello-world", "-", "hello-world")]
+    [TestCase("test_123", "_", "test_123")]
+    [TestCase("abc!@#def", "***", "abc*********def")]
+    public void ReplaceNonAlphanumericChars_String_ReplacesCorrectly(string input, string replacement, string expected)
+        => Assert.AreEqual(expected, input.ReplaceNonAlphanumericChars(replacement));
+}