CODEWITHSUNDEEP
c#unit-testingnunitconsole-application
Martin
Martin

Reputation: 24308

C# Unit Testing(Nunit) the Main method of a console app?

I have a question on unit testing the Main method of a console app. The standard signature is

  public static void Main(string[] args)

I want to be able to test to ensure that only 1 parameter is passed in. If more than one parameter is passed in that i want the test to fail.

I don't think i can mock this with MOQ as its a static method.

Anyone have any experience with this?

Any ideas ?

Thanks

Upvotes: 18

Views: 23221

Answers (2)

Artur INTECH
Artur INTECH

Reputation: 7276

Integration test

ProgramTest.cs

using NUnit.Framework;

namespace Tests;

public class ConsoleTests
{
    [Test]
    public void ProhibitsMoreThanOneArgument()
    {
        var capturedStdOut = CapturedStdOut(() =>
        {
            RunApp(arguments: new string[] { "argument1", "argument2" });
        });

        Assert.AreEqual("Passing two arguments is not supported.", capturedStdOut );
    }

    void RunApp(string[]? arguments = default)
    {
        var entryPoint = typeof(Program).Assembly.EntryPoint!;
        entryPoint.Invoke(null, new object[] { arguments ?? Array.Empty<string>() });
    }

    string CapturedStdOut(Action callback)
    {
        TextWriter originalStdOut = Console.Out;

        using var newStdOut = new StringWriter();
        Console.SetOut(newStdOut);

        callback.Invoke();
        var capturedOutput = newStdOut.ToString();

        Console.SetOut(originalStdOut);

        return capturedOutput;
    }
}

Implementation

Program.cs

if (args.Length > 1)
{
    Console.WriteLine("Passing two arguments is not supported.");
}

Upvotes: 3

k.m
k.m

Reputation: 31454

There is nothing to mock in your scenario. Static Program.Main is a method just as any other and you test it as such -- by invoking it.

The issue with static void method is that you can only verify whether it throws exception or interacts with input argument (or other static members, eventually). Since there is nothing to interact with on string[] you can test former case.

However, a more sound approach is to delegate all logic contained in Main to separate component and test it instead. Not only this allows you to test your input argument handling logic thoroughly but also simplifies Main to more or less this:

public static void Main(string[] args)
{
    var bootstrapper = new Bootstrapper();
    bootstrapper.Start(args);
}

Upvotes: 31

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