NSubstitute Returns method and arrays

Question

so I want to test roll results of dice set, but i can't pass an array as arg in Returns method like this:

    [TestCase(new[]{2, 2, 3, 1, 5}, Category.Yahtzee, 0)]
    public void AddPoints_ForGivenCategory_PointsAreStored(
        int[] rollResults, Category selectedCategory, int expectedScore)
    {
        _randomizer.GetRandomNumber(MIN_VALUE, MAX_VALUE).Returns(rollResults); //<-rollResults not allowed
        IDice[] dice = MakeNewDiceSet();

        _game.NewGame("A");
        _game.RollDice(dice);
        _game.AddPoints(selectedCategory);
        var result = _game.GameStatus().First()[selectedCategory];

        Assert.AreEqual(expectedScore, result);
    }

any tips or workarounds for this problem? Or am I forced to do this:

    [TestCase(2, 2, 3, 1, 5, Category.Yahtzee, 0)]
    public void AddPoints_ForGivenCategory_PointsAreStored(
        int die1, int die2, int die3, int die4, int die5, Category selectedCategory, int expectedScore)
    {
        _randomizer.GetRandomNumber(MIN_VALUE, MAX_VALUE).Returns(die1, die2, die3, die4, die5);
        IDice[] dice = MakeNewDiceSet();
        / ...
    }

Using NSubstitute v3.1.0.0

Answer 1

NSubstitute does not have Returns<T>(T[] values) (or similar). Instead it has Returns<T>(T initialValue, params T[] otherValues) to indicate we should always specify at least one value to return. The aim at the time was to avoid the potentially confusing case of stubbing a call with "no values" in the case of an empty collection. (Is it a no-op? Or does it clear the call?)

There are a few ways to get the behaviour you want. One way is to split the values into "first" and "rest":

random.GetRandomNumber(1, 10)
      .Returns(rollResults.First(), rollResults.Skip(1).ToArray());

Another approach is to use a Queue and stub GetRandomNumber() to consume this:

var rolls = new Queue<int>(rollResults);           
random.GetRandomNumber(1, 10).Returns(_ => rolls.Dequeue());

If this is something you need frequently it might be worth creating your own Returns extension that explicitly defines how the empty case should be handled.