Mocking in Unit Tests

Hi,

I am curious which frameworks exist to mock objects in unit tests. A quick  
search has led me to SmallMock, but what do you use? And why?

Regards, Steffen
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Mocking isn't commonly used in Smalltalk testing. In one of my courses I introduce SmallMock and get the students to play with it. My feeling is that mocking breaks encapsulation and makes the testcases specify assumptions which they shouldn't make. This makes the tests too brittle. A small change in the code may force you to change a number of tests to change your assumptions.

I also find that testing with mocks may give tests that pass when the real objects fail. Mocks assume they know how the real objects work. If the real objects work differently than the assumptions then the tests pass even though the real objects fail. This gives the tests some dangerous false positives.

I'd rather use stubs or real objects if possible. I generally find mocks too difficult to work with in unit testing.

David Buck

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-----Original Message-----
From: Steffen Märcker [hidden email]
Sender: [hidden email]
Date: Thu, 26 May 2011 11:43:10
To: vwnc<[hidden email]>
Subject: [vwnc] Mocking in Unit Tests

Hi,

I am curious which frameworks exist to mock objects in unit tests. A quick  
search has led me to SmallMock, but what do you use? And why?

Regards, Steffen
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On May 26, 2011, at 5:43 AM, Steffen Märcker wrote:

I can recommend "sMock" which is in the Cincom Public SToRE Repository.

David


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Yes, mocks seem to be not very popular among Smalltalkers. But I believe that's wrong. :)

I have been using this technique for several years in Smalltalk and I think I can affirm that it helps me to make TDD more consistent and "seamless" leading to a more modular and (if properly applied) clear design. Of course, mock tests must be combined with "classic" ones as they naturally complement each other at different steps of development.

Concerning tools for mocking, I use and highly recommend Mocketry (available for VW and Pharo/Squeak). Unlike SMocks, Mocketry allows to write expectations (very naturally) as message sends and provides a bunch of interesting and useful features for mocking and specifications. For example, famous Fowler's "Warehouse" example can be written as follows: 

OrderFillingTests >> testDoesNotRemoveInventoryIfNotEnoughInStock
 | order |
 order := Order on: 101 of: #article.
 [:warehouse |
   [order fillIn: warehouse] should strictly
     satisfy: [(warehouse has: 101 of: #article) willReturn: false]]
         runScenario.
 self deny: order isFilled

The warehouse parameter here is automatically initialized with a mock object. Sending #fillIn: to an order we expect the warehouse (we provided as parameter there) to be asked if it has the needed inventory. Here, we want it to answer "no" (prohibiting the order to be filled).

BTW, I am currently working on articles covering my experience with mocks and Mocketry, one of which I'd like to present at ESUG 2011 (if accepted of course, and able to afford necessary means to come there).

-- 
Dennis Schetinin

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On Friday, May 27, 2011, Sudhakar Krishnamachari
<[hidden email]> wrote:


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