Unit Testing with functions that return random results

Question

I don\'t think that this is specific to a language or framework, but I am using xUnit.net and C#.

I have a function that returns a random date in a certain range. I

Answer 1

Mock or fake out the random number generator

Do something like this... I didn't compile it so there might be a few syntax errors.

public interface IRandomGenerator
{
    double Generate(double max);
}

public class SomethingThatUsesRandom
{
    private readonly IRandomGenerator _generator;

    private class DefaultRandom : IRandomGenerator
    {
        public double Generate(double max)
        {
            return (new Random()).Next(max);
        }
    }

    public SomethingThatUsesRandom(IRandomGenerator generator)
    {
        _generator = generator;
    }

    public SomethingThatUsesRandom() : this(new DefaultRandom())
    {}

    public double MethodThatUsesRandom()
    {
        return _generator.Generate(40.0);
    }
}

In your test, just fake or mock out the IRandomGenerator to return something canned.