How to Repeat a return value

[Candy Chiu]

For a particular function, I need to return value1 for the first call, then value2 for all subsequent calls.  How do I specify this behavior?

           stub.Func().Returns(value1, Repeat(value2));

[David Tchepak]

stub.Func().Returns(value1, value2);

This will repeat value2 after it has returned value1.

On Wed, Feb 27, 2013 at 6:14 AM, Candy Chiu <candy....@gmail.com> wrote:

For a particular function, I need to return value1 for the first call, then value2 for all subsequent calls.  How do I specify this behavior?

           stub.Func().Returns(value1, Repeat(value2));

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[Candy Chiu]

David,

Is there a way to repeat the values other than the last one?

stub.Func().Returns(Repeat(value1, 3), Repeat(value2, 3), value3);

instead of 

stub.Func().Returns(value1, value1, value1, value2, value2, value2, value3);

Thanks.

[Candy Chiu]

Along the same line, how do I specify multiple Do's for When?

stub.WhenForAnyArgs(x => x.DoWork())

      .Do(x => CallbackForFirstCall())

      .Do(x => CallbackForSecondCall());

On Tuesday, February 26, 2013 6:22:02 PM UTC-5, David Tchepak wrote:

[Candy Chiu]

Just want to supplement the question with some background info.

I have functions that returns multiple values via either ref or out.  I need to specify each call's return value similar to how the regular Returns works.

Thanks. 

[David Tchepak]

First I need to put in the usual disclaimer about over-specifying tests. If you need this much real behaviour from a substitute you may be testing too much or you may be better using a real implementation (or a hand-rolled test double that behaves exactly how you want).

That said, you can get more control over what is returned by passing a function that manages it for you:

stub.Func().Returns(x => GetNextValue());

Here's an example of a structure that handles this for you:

    public interface IFoo { string Stuff(); }

    [Test]

    public void Example()

    {

        var foo = Substitute.For<IFoo>();

        var returns = ReturnsQueue<string>

            .FirstRepeat("hello", 2)

            .ThenRepeat("world", 3)

            .Then("!");

        foo.Stuff().Returns(x => returns.Next());

        for (int i = 0; i < 6; i++)

        {

            Console.WriteLine(foo.Stuff());

        }

        /* outputs:

        hello

        hello

        world

        world

        world

        !

        */ 

    }

    public class ReturnsQueue<T>

    {

        public static ReturnsQueue<T> FirstRepeat(T value, int times) { return new ReturnsQueue<T>().ThenRepeat(value, times); }

        public static ReturnsQueue<T> First(T value) { return new ReturnsQueue<T>().Then(value); } 

        private readonly Queue<Func<T>> _returns = new Queue<Func<T>>();

        private ReturnsQueue() { }

        public ReturnsQueue<T> Then(T value) { _returns.Enqueue(() => value); return this; }

        public ReturnsQueue<T> ThenRepeat(T value, int times)

        {

            foreach (var v in Enumerable.Repeat(value, times)) { Then(v); } 

            return this;

        }

        public T Next() { return _returns.Dequeue().Invoke(); }

    }

[David Tchepak]

NSubstitute doesn't support this. You'll need to add that logic into the callback itself.

[David Tchepak]

I think you could use a similar approach to the ReturnsQueue I posted earlier to set multiple ref/out values, with a different value set each time the queue.Next() is called.

Sound OK?

[David Tchepak]

Was just pointed out to me that this can be done more simply with the
Returns(T value, params T values) overload:

[Test]
public void Example2()
{

var foo = Substitute.For<IFoo>();

foo.Stuff().Returns("hello", Repeat("world",
3).Concat(Repeat("!", 2)).ToArray());

// produces: "hello", "world", "world", "world", "!", "!"
}

The queue approach may be useful for the different callback behaviours
required for your When..Do callbacks though, or if additional logic is
required to produce values for some reason.

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