StartsWith

using System.Diagnostics;
using Xunit.Abstractions;

[assembly: CollectionBehavior(DisableTestParallelization = true)]

// Remove "static" from "public static unsafe class StringTests"

    [Fact]
    public void TestStartsWithPerfMatch1Char()
    {
        string test2 = "abc";
        bool result;

        Profile("StartsWith Perf Match Char", 10000000, () =>
        {
            result = test2.StartsWith("a", StringComparison.Ordinal);
        });
    }

    [Fact]
    public void TestStartsWithPerfMatch2Char()
    {
        string test1 = "abc";
        bool result;
        
        Profile("StartsWith Perf Match String", 10000000, () =>
        {
            result = test1.StartsWith("ab", StringComparison.Ordinal);
        });
    }

    [Fact]
    public void TestStartsWithPerfNoMatchFirstChar()
    {
        string test1 = "abc";
        bool result;

        Profile("StartsWith Perf No-Match first char", 10000000, () =>
        {
            result = test1.StartsWith("X", StringComparison.Ordinal);
        });
    }

    [Fact]
    public void TestStartsWithPerfNoMatch()
    {
        string test1 = "abc";
        bool result;

        Profile("StartsWith Perf No-Match", 10000000, () =>
        {
            result = test1.StartsWith("aX", StringComparison.Ordinal);
        });
    }

    private readonly ITestOutputHelper output;

    public StringTests(ITestOutputHelper output)
    {
        this.output = output;
    }
    
    void Profile(string description, int iterations, Action func)
    {
        // warm up 
        func();
        // clean up
        GC.Collect();
        
        var watch = new Stopwatch();
        watch.Start();
        for (int i = 0; i < iterations; i++)
        {
            func();
        }

        watch.Stop();
        output.WriteLine(description);
        output.WriteLine(" Time Elapsed {0} ms", watch.ElapsedMilliseconds);
    }