Add test for ReadOnlySpan.Count extension

tests/Jellyfin.Controller.Tests/Extensions/StringExtensionsTests.cs

@@ -0,0 +1,19 @@
+using System;
+using MediaBrowser.Controller.Extensions;
+using Xunit;
+
+namespace Jellyfin.Controller.Extensions.Tests
+{
+    public class StringExtensionsTests
+    {
+        [Theory]
+        [InlineData("", '_', 0)]
+        [InlineData("___", '_', 3)]
+        [InlineData("test\x00", '\x00', 1)]
+        [InlineData("Imdb=tt0119567|Tmdb=330|TmdbCollection=328", '|', 2)]
+        public void ReadOnlySpan_Count_Success(string str, char needle, int count)
+        {
+            Assert.Equal(count, str.AsSpan().Count(needle));
+        }
+    }
+}