I'm using Rhino Mocks to try to verify that when I call a certain method, that the method in turn will properly group items and then call another method.

Something like this:

//Arrange
var bucketsOfFun = new BucketGame();

var balls = new List<IBall>
                {
                    new Ball { Color = Color.Red },
                    new Ball { Color = Color.Blue },
                    new Ball { Color = Color.Yellow },
                    new Ball { Color = Color.Orange },
                    new Ball { Color = Color.Orange }
                };

//Act
bucketsOfFun.HaveFunWithBucketsAndBalls(balls);

//Assert ???

Here is where the trouble begins for me. My method is doing something like this:

public void HaveFunWithBucketsAndBalls(IList<IBall> balls)
{
    //group all the balls together according to color
    var blueBalls = GetBlueBalls(balls);
    var redBalls = GetRedBalls(balls);
    // you get the idea

    HaveFunWithABucketOfBalls(blueBalls);
    HaveFunWithABucketOfBalls(redBalls);
    // etc etc with all the different colors
}

public void HaveFunWithABucketOfBalls(IList<IBall> colorSpecificBalls)
{
    //doing some stuff here that i don't care about 
    //for the test i'm writing right now
}

What I want to assert is that each time I call HaveFunWithABucketOfBalls that I'm calling it with a group of 1 red ball, then 1 blue ball, then 1 yellow ball, then 2 orange balls.

If I can assert that behavior then I can verify that the method is doing what I want it to do, which is grouping the balls properly.

Any ideas of what the best testing pattern for this would be?