added sample tests from mbedded sample code

tests/CommandLine.Tests/Unit/Issue389_Tests.cs

@@ -0,0 +1,78 @@
+using CommandLine.Text;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Xunit;
+
+namespace CommandLine.Tests.Unit
+{
+
+	public class Issue389_Tests
+	{
+
+		private const int ERROR_SUCCESS = 0;
+
+		// Test method (xUnit) which fails
+		[Fact]
+		public void CallMain_GiveHelpArgument_ExpectSuccess()
+		{
+			var result = Program.__Main(new[] { "--help" });
+
+			Assert.Equal(ERROR_SUCCESS, result);
+		}
+
+		// main program
+		internal class Program
+		{
+
+
+			internal static int __Main(string[] args)
+			{
+				bool hasError = false;
+				bool helpOrVersionRequested = false;
+
+				ParserResult<Options> parsedOptions = Parser.Default.ParseArguments<Options>(args)
+					.WithNotParsed(errors => {
+						helpOrVersionRequested = errors.Any(
+							x => x.Tag == ErrorType.HelpRequestedError 
+							|| x.Tag == ErrorType.VersionRequestedError);
+					hasError = true;
+				});
+
+				if(helpOrVersionRequested)
+				{
+					return ERROR_SUCCESS;
+				}
+
+				// Execute as a normal call
+				// ...
+				return ERROR_SUCCESS;
+			}
+
+		}
+
+		// Options
+		internal class Options
+		{
+
+			[Option('c', "connectionString", Required = true, HelpText = "Texts.ExplainConnection")]
+			public string ConnectionString { get; set; }
+
+			[Option('j', "jobId", Required = true, HelpText = "Texts.ExplainJob")]
+			public int JobId { get; set; }
+
+			[Usage(ApplicationAlias = "Importer.exe")]
+			public static IEnumerable<Example> Examples
+			{
+				get => new[] {
+				  new Example("Texts.ExplainExampleExecution", new Options() {
+					  ConnectionString="Server=MyServer;Database=MyDatabase",
+					  JobId = 5
+				  }),
+			  };
+			}
+
+		}
+	}
+}