добавил пример бенчмарка

Testing/Advanced/Advanced.csproj

@@ -8,6 +8,7 @@
 
   <ItemGroup>
     <PackageReference Include="ApprovalTests" Version="6.0.0" />
+    <PackageReference Include="BenchmarkDotNet" Version="0.14.0" />
     <PackageReference Include="FakeItEasy" Version="8.3.0" />
     <PackageReference Include="FluentAssertions" Version="6.12.0" />
     <PackageReference Include="log4net" Version="2.0.17" />

Testing/Advanced/Samples/4. PerformanceTests/Benchmark.cs

@@ -0,0 +1,83 @@
+namespace Advanced.Samples.Performance;
+
+
+using BenchmarkDotNet.Attributes;
+using BenchmarkDotNet.Configs;
+using BenchmarkDotNet.Running;
+using FluentAssertions;
+using NUnit.Framework;
+
+[MemoryDiagnoser(true)]
+public class Benchmarks
+{
+    private const long num = long.MaxValue;
+
+    [Benchmark]
+    public void GetDigitsFromLeastSignificant_String()
+    {
+        num
+            .ToString()
+            .Select(x => Convert.ToByte(x.ToString()))
+            .ToArray();
+    }
+
+    [Benchmark]
+    public void GetDigitsFromLeastSignificant_MathWithSpan()
+    {
+        var result = new byte[20];
+        var span = new Span<byte>(result);
+        var n = num;
+        var index = 0;
+        while (n > 0)
+        {
+            span[index] = (byte)(n % 10);
+            n /= 10;
+            index++;
+        }
+
+        var res = span[..index].ToArray();
+    }
+
+    [Benchmark]
+    public void GetDigitsFromLeastSignificant_MathWithList()
+    {
+        var result = new List<byte>();
+        var n = num;
+        while (n > 0)
+        {
+            result.Add((byte)(n % 10));
+            n /= 10;
+        }
+    }
+
+    [Benchmark]
+    public void GetDigitsFromLeastSignificant_MathWithYield()
+    {
+        IEnumerable<byte> Inner()
+        {
+            var n = num;
+            while (n > 0)
+            {
+                yield return (byte)(n % 10);
+                n /= 10;
+            }
+        }
+
+        Inner().ToArray();
+    }
+}
+
+[TestFixture]
+[Explicit]
+public class BenchmarkTests
+{
+    [Test]
+    public void GetDigitsFromLeastSignificant()
+    {
+        var config = ManualConfig
+            .CreateMinimumViable()
+            .WithOption(ConfigOptions.DisableOptimizationsValidator, true);
+
+        BenchmarkRunner.Run<Benchmarks>(config);
+    }
+}