Question

I have the following method, which I want to perform a unit test on. Change can be made for the method signature:

public void PrintNumber()
{
    Enumerable.Range(1, 100).ToList().ForEach(x =>
    {
        if (x % 3 == 0 && x % 5 == 0)
            Console.WriteLine("[35]");
        else if (x % 3 == 0)
            Console.WriteLine("[3]");
        else if (x % 5 == 0)
            Console.WriteLine("[5]");
        else
            Console.WriteLine(x.ToString());
    });
}

I have my own solution, but I want to find out if my version is the best.

Thanks!

Answer 1

In order to unit test this method, you need to wrap your Console.WriteLine() with a proxy class, and inject that class into your method.

public interface IWriter
{
    void Write(string text);
}

public class ConsoleWriter : IWriter
{
    public void Write(string text)
    {
       Console.WriteLine(text);
    }
}

public class StubWriter : IWriter
{
    List<string> values = new List<string>();
    public void Write(string text)
    {
         values.Add(text);
    }

    public List<string> Values { get { return values; } }
}

With this structure you change your method signature to PrintNumber(IWriter writer) and call the writer. In your test method you inject the StubWriter, in production you inject the ConsoleWriter.