Question

I want to substitute object to return sequence of different objects.
For example:

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

will return resourceString then resourceString2 then exception.

Or something like this:

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

will return resourceString then exception then resourceString2.

How can I do that?

Answer 1

This answer is outdated — NSubstitute has direct support for this now.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.