How would you test this?

[Louis Rose-2]

Hi all,

I'm new to jMock, and am exploring the limits of what it can and can't
do. I've recently discovered a pattern that I'm struggling to test with
jMock. I'll present an example, and I hope you can show me how you'd
test this. I suspect I need to adjust my approach to use jMock in this
situation. Thanks in advance!

Suppose we have a TrackImpl class, which has an attribute, circuit of
type List<Point>. Point has a subclass, SpeedPoint. We wish to add a
method to Track, getPreviousSpeedPoint(Point current). The new method will:

- return the nearest previous SpeedPoint in circuit to the given parameter.
- wrap around to find the nearest previous SpeedPoint. (For example,
current could be at index 0, and a SpeedPoint at index circuit.size() -
1. In that case, the SpeedPoint at circuit.size() - 1 should be returned).
- return null if no SpeedPoints are found in circuit.
- throw an IllegalArgumentException if current is not contained in circuit.

I hope this explanation is clear! I'd be interested in seeing your tests
for the first couple of bullet points.

I feel like I should be stubbing out Track#getCircuit() by subclassing
TrackImpl. Is a different approach used with jMock?

Many thanks in advance.

Cheers,
Louis.

----
Louis Rose
Research Student
Department of Computer Science,
University of York,
Heslington, York, YO10 5DD, United Kingdom.
[phone]
Twitter: @louismrose

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[Steve Freeman-2]

I don't see what needs to be mocked in this scenario. What is the  
collaborating object that should be replaced?

S.

On 22 May 2009, at 10:23, Louis Rose wrote:

> Hi all,
>
> I'm new to jMock, and am exploring the limits of what it can and  
> can't do. I've recently discovered a pattern that I'm struggling to  
> test with jMock. I'll present an example, and I hope you can show me  
> how you'd test this. I suspect I need to adjust my approach to use  
> jMock in this situation. Thanks in advance!
>
> Suppose we have a TrackImpl class, which has an attribute, circuit  
> of type List<Point>. Point has a subclass, SpeedPoint. We wish to  
> add a method to Track, getPreviousSpeedPoint(Point current). The new  
> method will:
>
> - return the nearest previous SpeedPoint in circuit to the given  
> parameter.
> - wrap around to find the nearest previous SpeedPoint. (For example,  
> current could be at index 0, and a SpeedPoint at index  
> circuit.size() - 1. In that case, the SpeedPoint at circuit.size() -  
> 1 should be returned).
> - return null if no SpeedPoints are found in circuit.
> - throw an IllegalArgumentException if current is not contained in  
> circuit.
>
> I hope this explanation is clear! I'd be interested in seeing your  
> tests for the first couple of bullet points.
>
> I feel like I should be stubbing out Track#getCircuit() by  
> subclassing TrackImpl. Is a different approach used with jMock?
>
> Many thanks in advance.
>
> Cheers,
> Louis.
>
> ----
> Louis Rose
> Research Student
> Department of Computer Science,
> University of York,
> Heslington, York, YO10 5DD, United Kingdom.
> [phone]
> Twitter: @louismrose
>
> ---------------------------------------------------------------------
> To unsubscribe from this list, please visit:
>
>   http://xircles.codehaus.org/manage_email
>
>

Steve Freeman
Winner of the Agile Alliance Gordon Pask award 2006

http://www.m3p.co.uk

M3P Limited.
Registered office. 2 Church Street, Burnham, Bucks, SL1 7HZ.
Company registered in England & Wales. Number 03689627



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[Louis Rose-2]

Hi Steve,

Thanks for the insightful question - I can use it in other situations to
determine whether to use a mock.

I agree that, in this case, there doesn't seem to be a collaborating
object. This example wasn't as good as I initially thought, I'm sorry.

I'm still a little confused about whether jMock can be used to stub out
methods on the object under test? I guess not. Does wanting to stub out
a method on the object under test indicate a problem with the design?

I'll post a better example if I stumble across one.

Many thanks for the help.

Cheers,
Louis.

Steve Freeman wrote:

> I don't see what needs to be mocked in this scenario. What is the
> collaborating object that should be replaced?
>
> S.
>
> On 22 May 2009, at 10:23, Louis Rose wrote:
>> Hi all,
>>
>> I'm new to jMock, and am exploring the limits of what it can and can't
>> do. I've recently discovered a pattern that I'm struggling to test
>> with jMock. I'll present an example, and I hope you can show me how
>> you'd test this. I suspect I need to adjust my approach to use jMock
>> in this situation. Thanks in advance!
>>
>> Suppose we have a TrackImpl class, which has an attribute, circuit of
>> type List<Point>. Point has a subclass, SpeedPoint. We wish to add a
>> method to Track, getPreviousSpeedPoint(Point current). The new method
>> will:
>>
>> - return the nearest previous SpeedPoint in circuit to the given
>> parameter.
>> - wrap around to find the nearest previous SpeedPoint. (For example,
>> current could be at index 0, and a SpeedPoint at index circuit.size()
>> - 1. In that case, the SpeedPoint at circuit.size() - 1 should be
>> returned).
>> - return null if no SpeedPoints are found in circuit.
>> - throw an IllegalArgumentException if current is not contained in
>> circuit.
>>
>> I hope this explanation is clear! I'd be interested in seeing your
>> tests for the first couple of bullet points.
>>
>> I feel like I should be stubbing out Track#getCircuit() by subclassing
>> TrackImpl. Is a different approach used with jMock?
>>
>> Many thanks in advance.
>>
>> Cheers,
>> Louis.
>>
>> ----
>> Louis Rose
>> Research Student
>> Department of Computer Science,
>> University of York,
>> Heslington, York, YO10 5DD, United Kingdom.
>> [phone]
>> Twitter: @louismrose
>>
>> ---------------------------------------------------------------------
>> To unsubscribe from this list, please visit:
>>
>>   http://xircles.codehaus.org/manage_email
>>
>>
>
> Steve Freeman
> Winner of the Agile Alliance Gordon Pask award 2006
>
> http://www.m3p.co.uk
>
> M3P Limited.
> Registered office. 2 Church Street, Burnham, Bucks, SL1 7HZ.
> Company registered in England & Wales. Number 03689627
>
>
>
> ---------------------------------------------------------------------
> To unsubscribe from this list, please visit:
>
>    http://xircles.codehaus.org/manage_email
>
>

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[Steve Freeman-2]

On 22 May 2009, at 11:47, Louis Rose wrote:
> Hi Steve,
>
> Thanks for the insightful question - I can use it in other  
> situations to determine whether to use a mock.

that's one of our core design questions.

> I'm still a little confused about whether jMock can be used to stub  
> out methods on the object under test? I guess not. Does wanting to  
> stub out a method on the object under test indicate a problem with  
> the design?

We think so, although plenty of others disagree. We prefer to think in  
terms of small objects composed together, rather than taking slices  
through larger objects.

> Many thanks for the help.


Always happy to help. In the meantime, we have a book in progress at

http://www.mockobjects.com/book

Read and comment via the list :)

S.

Steve Freeman
Winner of the Agile Alliance Gordon Pask award 2006

http://www.m3p.co.uk

M3P Limited.
Registered office. 2 Church Street, Burnham, Bucks, SL1 7HZ.
Company registered in England & Wales. Number 03689627



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