The writer should write to stderr

Question

public static class Utils
{
    /// <summary>
    /// Creates a Writer object that writes either to a file or to a console stream.
    /// </summary>
    /// <param name="outFname">file name, "stdout" or "stderr"</param>
    /// <param name="ifAppend">if true, append to existing file; otherwise, overwrite</param>
    /// <returns>A TextWriter object that can be used to write output.</returns>
    public static StreamWriter OutWriter(string outFname, bool ifAppend)
    {
        if (string.IsNullOrEmpty(outFname) || outFname == "stdout")
        {
            return new StreamWriter(Console.OpenStandardOutput());
        }
        else if (outFname == "stderr")
        {
            return new StreamWriter(Console.OpenStandardError());
        }
        else
        {
            FileStream fileStream;
            if (ifAppend)
                fileStream = new FileStream(outFname, FileMode.Append, FileAccess.Write, FileShare.None);
            else
                fileStream = new FileStream(outFname, FileMode.Create, FileAccess.Write, FileShare.None);
            return new StreamWriter(fileStream, Encoding.UTF8);
        }
    }
}

[TestMethod]
public void OutWriter_ShouldReturnConsoleError_ForStderr()
{
    // Capture the current Console.Error
    TextWriter originalError = Console.Error;

    // Redirect Console.Error to a StringWriter to capture the output
    StringWriter errorWriter = new StringWriter();
    Console.SetError(errorWriter);

    using (StreamWriter writer = Utils.OutWriter("stderr", false))
    {
        // Write something to the StreamWriter
        writer.WriteLine("Test error output");
        writer.Flush(); // Ensure the output is flushed
    }

    // Reset the Console.Error to its original state
    Console.SetError(originalError);

    // Verify that the output was written to the StringWriter
    string expectedOutput = "Test error output" + Environment.NewLine;
    string actualOutput = errorWriter.ToString();
    Assert.AreEqual(expectedOutput, actualOutput, "The writer should write to Console.Error.");
}

Test output:

Test Name:  OutWriter_ShouldReturnConsoleError_ForStderr
Test FullName:  PdbLibTests.UtilsTests.OutWriter_ShouldReturnConsoleError_ForStderr
Test Source:    C:\git\MyProject_csharp\unit_test_for_Utils\UtilsTests.cs : line 15
Test Outcome:   Failed
Test Duration:  0:00:00.1644456

Result StackTrace:  at PdbLibTests.UtilsTests.OutWriter_ShouldReturnConsoleError_ForStderr() in C:\git\MyProject_csharp\unit_test_for_Utils\UtilsTests.cs:line 37
Result Message: 
Assert.AreEqual failed. Expected:<Test error output
>. Actual:<>. The writer should write to Console.Error.

Why isn't the unit-test succeeding?

How can I make it succeed?

---

Then I tried mocking the console:

public static class MockConsole
{
    public static StringWriter ErrorWriter { get; private set; }
    public static TextWriter OriginalError { get; private set; }

    public static void Initialize()
    {
        OriginalError = Console.Error;
        ErrorWriter = new StringWriter();
        Console.SetError(ErrorWriter);
    }

    public static void Reset()
    {
        Console.SetError(OriginalError);
        ErrorWriter.Dispose();
    }
}


[TestMethod]
public void OutWriter_ShouldReturnConsoleError_ForStderr()
{
    // Initialize mock console
    MockConsole.Initialize();

    using (StreamWriter writer = Utils.OutWriter("stderr", false))
    {
        // Write something to the StreamWriter
        writer.WriteLine("Test error output");
        writer.Flush(); // Ensure the output is flushed
    }

    // Capture the output written to the error writer
    string actualOutput = MockConsole.ErrorWriter.ToString();

    // Reset the console to its original state
    MockConsole.Reset();

    // Verify that the output was written to the StringWriter
    string expectedOutput = "Test error output" + Environment.NewLine;
    Assert.AreEqual(expectedOutput, actualOutput, "The writer should write to Console.Error.");
}

This also hasn't succeeded.

Answer 1

I just checked the implementation: Console.OpenStandardError() opens a (new) standard error stream, regardless of what it was before. Use the Console.Error property to get the mock object you have assigned using Console.SetError().