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

55
votes

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?

2
c#unit-testingconsolenunit
That is an integration test and not a unit test. – Oliver Hanappi
I agree, I'm reworking the solution layout to reflect that right now. – Lasse V. Karlsen
Though it is in sort of a gray area, I am not actually invoking any external program, just calling code in my program file, but I still think it is more like an integration test than a unit test. – Lasse V. Karlsen

2 Answers

89
votes

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.

20
votes

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.