Rhino Mocks - mocking a method whose return value changes (even when passed the same parameter) with multiple calls

Question

I'm looking to find out how I can mock a method that returns a different value the second time it is called to the first time. For example, something like this:

public interface IApplicationLifetime
{
    int SecondsSinceStarted {get;}
}

[Test]
public void Expected_mock_behaviour()
{
    IApplicationLifetime mock = MockRepository.GenerateMock<IApplicationLifetime>();

    mock.Expect(m=>m.SecondsSinceStarted).Return(1).Repeat.Once();
    mock.Expect(m=>m.SecondsSinceStarted).Return(2).Repeat.Once();

    Assert.AreEqual(1, mock.SecondsSinceStarted);
    Assert.AreEqual(2, mock.SecondsSinceStarted);
}

Is there anything that makes this possible? Besides implementing a sub for the getter that implements a state machine?

Take a look at ordered and unordered mocks: http://ayende.com/wiki/Rhino%20Mocks%20Ordered%20and%20Unordered.ashx — Maciej, May 23 '12 at 13:44
Whats wrong with code you provided? `Repeat.Once()` should work — Sergey Berezovskiy, May 23 '12 at 14:56
@lazyberezovsky The first call to m.SecondsSinceStarted returns 2, not 1 as expected — AlexC, May 23 '12 at 15:14
@AlexC can you provide real test code? Because `Repeat.Once()` will return 1 during first call — Sergey Berezovskiy, May 23 '12 at 15:29
@lazyberezovsky The code above is real. If I run it with the latest build of RhinoMocks (after replacing m.SecondsSinceStarted with mock.SecondsSinceStarted inside the Asserts - a silly error) then the test fails with: Expected: 1 But was: 2 — AlexC, May 23 '12 at 16:12
FFFFFFFUUUUUUUUUUUU... If I *run* the test it passes. If I *debug and step through* it fails. Must be evaluating the mock's properties in my locals window or something... — AlexC, May 23 '12 at 16:18

score 37 · Accepted Answer · edited Sep 01 '20 at 00:38

37

You can intercept return values with the .WhenCalled method. Note that you still need to provide a value via the .Return method, however Rhino will simply ignore it if ReturnValue is altered from the method invocation:

int invocationsCounter = 1;
const int IgnoredReturnValue = 10;
mock.Expect(m => m.SecondsSinceLifetime)
    .WhenCalled(mi => mi.ReturnValue = invocationsCounter++)
    .Return(IgnoredReturnValue);

Assert.That(mock.SecondsSinceLifetime, Is.EqualTo(1));
Assert.That(mock.SecondsSinceLifetime, Is.EqualTo(2));

Digging around a bit more, it seems that .Repeat.Once() does indeed work in this case and can be used to achieve the same result:

mock.Expect(m => m.SecondsSinceStarted).Return(1).Repeat.Once();
mock.Expect(m => m.SecondsSinceStarted).Return(2).Repeat.Once();
mock.Expect(m => m.SecondsSinceStarted).Return(3).Repeat.Once();

Will return 1, 2, 3 on consecutive calls.

edited Sep 01 '20 at 00:38

Peter Mortensen

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answered May 23 '12 at 13:44

k.m

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As I understand, for something other than sequential numbers he should create array and return values by index? – Sergey Berezovskiy May 23 '12 at 14:46
I agree that this method works, but this is essentially the same as having to implement a state machine, which I mentioned I am trying to avoid (i.e. if I wanted to return 11 on the second call, then I'd need to do something like "if (invocationsCounter == 1) return 1; else if (invocationsCounter == 2) return 11;" which looks very much like a state machine. – AlexC May 23 '12 at 15:08
Re: your edit. Not sure if this is some functionality that has changed in the version of RhinoMocks that I am using and the one you are using, but I have run the test that is in my original question, and can tell you it fails (i.e. the first call to SecondsSinceStarted returns 2). Have you got a link to where you found that it does work? – AlexC May 23 '12 at 15:25
Seems the problem was carelessness on my part - test passes if I run, but fails if I step through, probably evaluating the property for a watch window somewhere. Answer accepted, ta. – AlexC May 23 '12 at 16:20

score 7 · Answer 2 · edited Sep 01 '20 at 00:40

7

Simply use

mock.Expect(m=>m.SecondsSinceStarted).Return(1).Repeat.Once();
mock.Expect(m=>m.SecondsSinceStarted).Return(2).Repeat.Once();

This will return 1 during the first call, and 2 during the second call. At least in Rhino Mocks 3.6.0.0.

edited Sep 01 '20 at 00:40

Peter Mortensen

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answered May 23 '12 at 15:30

Sergey Berezovskiy

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This certainly conflicts with what I see when I run the test above – AlexC May 23 '12 at 16:16
As mentioned in the accepted answer, this is correct, my test was only failing as I was stepping through and evaluating something inadvertently. Upvoted. – AlexC May 23 '12 at 16:21

score 0 · Answer 3 · edited Sep 01 '20 at 00:39

0

If time is the determining factor in what the method returns, I would try to abstract out the time passage so you have direct control over it in your tests.

Something like an interface called ITimeProvider with a member called GetElapsedTime() and then create a default implementation to use throughout your application.

Then when you are testing, pass in a mocked ITimeProvider so you control what is perceived by your application to be time passed.

edited Sep 01 '20 at 00:39

Peter Mortensen

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answered May 23 '12 at 14:26

theMothaShip

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Really, the time thing was just a handy example without fully describing what it is i'm trying to test. Even so, though, if I wanted to mock an ITimeProvider, which had a GetElapsedTime() method, the problem would still exist if I wanted to write a unit test which called GetElapsedTime() twice, and wanted my mock ITimeProvider to return a different time for each call. – AlexC May 23 '12 at 15:12
Could you have the ITimeProvider be a property dependancy? Thus being able to inject new mocks before each call? Even so, if its not time you're dealing with, my answer is probably worthless... – theMothaShip May 23 '12 at 15:18
My question was more about whether RhinoMocks supports this kind of interaction with generated mocks/stubs, and less about how I might work around it, should it not be supported. Thanks though. – AlexC May 23 '12 at 15:22

Rhino Mocks - mocking a method whose return value changes (even when passed the same parameter) with multiple calls

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