Assertion.cs

public class Program
{
    static void Main(string[] args)
    {
        string str = "Hello work!";
        Test(str,
            error =>
            {
                Console.WriteLine(error.Message);
                Console.ReadLine();
            });
    }
    
    static void Test(string str, Action<Exception> a)
    {
        var error = str
        
        .Assert("Length == 11"
                s => s.Length == 11,        () => str

        .Assert("Starts with \"Hello\"",
                s => s.StartsWtih("Hello"), () => str

        .Assert("Ends with \"world!\"",
                s => s.EndsWith("world!"),  () =>

        Assertion.End)));
        
        if (error != null) a(error);
    }
}

public static class Assertion
{
    private Func<string, Exception> fail =
        msg => new Exception(msg);
    public static Func<Exception> End = () =>
        { return null; }
    public static Exception Assert<T>(
        this T obj,
        string description,
        Predicate<T> predicate,
        Func<Exception> continuation)
    {
        return predicate.Invoke(obj)
            ? continuation()
            : fail("\"" + description + "\" failed.");
    }
}