NSubstitute multiple return sequence

This answer is outdated — NSubstitute has direct support for this now. Please see @dangerdex's answer to this question for more information.

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The multiple returns syntax in NSubstitute only supports values. To also throw exceptions you'll need to pass a function to Returns, and implement the required logic yourself (e.g. Returns(x => NextValue())).

There is a related example for Moq sequences on Haacked's blog using a queue. You can do a similar thing with NSubstitute (example code only, use at your own risk :)):

public interface IFoo { int Bar(); }

[Test]
public void Example() {
    var results = new Results<int>(1)
                    .Then(2)
                    .Then(3)
                    .Then(() => { throw new Exception("oops"); });
    var sub = Substitute.For<IFoo>();
    sub.Bar().Returns(x => results.Next());

    Assert.AreEqual(1, sub.Bar());
    Assert.AreEqual(2, sub.Bar());
    Assert.AreEqual(3, sub.Bar());
    Assert.Throws<Exception>(() => sub.Bar());
}

public class Results<T> {
    private readonly Queue<Func<T>> values = new Queue<Func<T>>();
    public Results(T result) { values.Enqueue(() => result); }
    public Results<T> Then(T value) { return Then(() => value); }
    public Results<T> Then(Func<T> value) {
        values.Enqueue(value);
        return this;
    }
    public T Next() { return values.Dequeue()(); }
}

Hope this helps.

Here's an example that does everything inline without an extra class. If you were doing this a lot I would probably go with the separate class option.

[Test]
public void WhenSomethingHappens()
{
    var something = Substitute.For<ISomething>();
    int callCount = 0;
    something.SomeCall().Returns(1, 2);
    something.When(x => x.SomeCall()).Do(obj => { if (++callCount == 3) throw new Exception("Problem!"); });

    Assert.AreEqual(1, something.SomeCall());
    Assert.AreEqual(2, something.SomeCall());
    Assert.Throws<Exception>(() => something.SomeCall());
}


public interface ISomething
{
    int SomeCall();
}

This is now a supported feature in NSubstitute with a very friendly interface.

It would be something like...

var http = Substitute.For<IHttp>();
http.GetResponse(Arg.Any<string>()).Returns(
  x => resourceString,
  x => resourceString2,
  x => { throw new Exception(); }
);

Documentation can be found here