CODEWITHSUNDEEP
c#unit-testingconsolenunit
Lasse V. Karlsen
Lasse V. Karlsen

Reputation: 391556

Grabbing the output sent to Console.Out from within a unit test?

I am building a unit test in C# with NUnit, and I'd like to test that the main program actually outputs the right output depending on the command line arguments.

Is there a way from an NUnit test method that calls Program.Main(...) to grab everything written to Console.Out and Console.Error so that I can verify against it?

Upvotes: 60

Views: 28475

Answers (3)

Artur INTECH
Artur INTECH

Reputation: 7396

You still need an integration test, not unit, as others have correctly suggested.

Integration test

ProgramTest.cs

using NUnit.Framework;

class ConsoleTests
{
    [Test]
    public void TestsStdOut()
    {
        var capturedStdOut = CapturedStdOut(() =>
        {
            RunApp();
        });

        Assert.AreEqual("Welcome, John!", 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

Console.Write($"Welcome, John!");

Upvotes: 1

Mark Seemann
Mark Seemann

Reputation: 233277

You can redirect Console.In, Console.Out and Console.Error to custom StringWriters, like this

[TestMethod]
public void ValidateConsoleOutput()
{
    using (StringWriter sw = new StringWriter())
    {
        Console.SetOut(sw);

        ConsoleUser cu = new ConsoleUser();
        cu.DoWork();

        string expected = string.Format("Ploeh{0}", Environment.NewLine);
        Assert.AreEqual<string>(expected, sw.ToString());
    }
}

See this blog post for full details.

Upvotes: 93

Vasil Trifonov
Vasil Trifonov

Reputation: 1867

You can use this simple class to get the output with a using statement:

public class ConsoleOutput : IDisposable
{
    private StringWriter stringWriter;
    private TextWriter originalOutput;

    public ConsoleOutput()
    {
        stringWriter = new StringWriter();
        originalOutput = Console.Out;
        Console.SetOut(stringWriter);
    }

    public string GetOuput()
    {
        return stringWriter.ToString();
    }

    public void Dispose()
    {
        Console.SetOut(originalOutput);
        stringWriter.Dispose();
    }
}

Here is an example how to use it:

using (var consoleOutput = new ConsoleOutput())
{
    target.WriteToConsole(text);

    Assert.AreEqual(text, consoleOutput.GetOuput());
}

you can find more detailed information and a working code sample on my blog post here - Getting console output within a unit test.

Upvotes: 23

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