News about mockA

The current release of mockA is available at Github. It contains an error fix that I would like to outline in today´s blog post.


The bug

MockA allows you to mock classes as described in one of my previous blog posts. Technically, mockA tries to create a subclass of the class which is subject to the mock creation. This means, it will only work, if the class is not marked as final and has a constructor which is at least protected or public.

MockA overrides methods that should be mocked, with a local implementation that returns the values expected to be returned. It follows the specifications set up by the unit test, according to the method( ), with( ) and exports( ) or returns( ) -calls (and so on) during mock creation.


There is another feature that reuses generated subroutine pools that have been created by mockA, because the Web Application Server ABAP allows only about 36 subroutine pools for each program, or, in our case, per unit test. The generated code does not contain any hard coded method output parameters as there would be no benefit in buffering the generated coding then. Instead, the instance of type ZIF_MOCKA_MOCKER is passed to the mock object. In the mock object´s method implementations, the fake values are read from that instance. If a new mock object should be created, a new instance of ZIF_MOCKA_MOCKER will be passed to the mock object. Hence, the method output may change.


If mockA generates the local implementation of an interface, each method is implemented during the initial mock class generation, so this feature poses no issues here.

However, in case a class needs to be mocked, mockA also tried to reuse these generated subroutine pools in the past. Do you see the error?


What could possibly happen

Imagine, mockA should create a mock implementation of the following class: ZCL_I_CAUSE_TROUBLE which has two methods:


  In our first unit test, we will tell mockA to simulate the output of METHOD_A, without defining any output for METHOD_B. 

When the mock object is created, mockA will generate a local subclass of ZCL_I_WILL_CAUSE_TROUBLE, with a local implementation of method METHOD_A that overrides the parent´s class method. The parent´s class method cannot be called any longer via the mock object. METHOD_B_ remains untouched.

After generation of the subroutine pool, the class implementation is buffered for later usage.


If another unit test, that is executed after the first one, wants to control the output of METHOD_B, mockA won´t return that output, as the method has not been overridden in the first unit test and therefore no output control takes place in the locally created class implementation: The logic that is responsible for returning the specified fake values is simply not called. Instead, the super implementation of ZCL_I_WILL_CAUSE_TROUBLE is called.


The solution

Subroutine pool buffering is now generally switched off if a class needs to be simulated. For interfaces, the current logic remains unchanged.

Unfortunately, this change is a breaking change, which can lead to failing unit tests, which have passed in the past.

This change could cause some new issues that I would like to outline briefly:

  1. Subroutine pool limits might be violated for existing unit tests. As there might be multiple implementations generated per class within the same unit test report, the subroutine pool limit might be violated once you updated mockA. In this case, please split up your test methods into various reports, if possible.
  2. Please see the example above: If your second unit test tells mockA to simulate the output of METHOD_B, but actually expects a result that is returned by the super implementation, your unit test might fail now, as the super implementation is not called any longer due to the correction and instead, the specified fake values will be returned.
    I know that this is just a theoretical consideration but important to be mentioned. Nevertheless, these test cases can be considered incorrectly implemented, as the unit test possibly expects other values than the values that have been defined as output for METHOD_B. Hence, these test cases should be reviewed anyway!


Feedback welcomed

There is no possibility to switch off the currently implemented behaviour of mockA as I think it is more important to fix the error than to allow old and incorrect unit test implementations not to fail.


Please let me know, if you run into trouble with the new update, and if issue 1) or 2) applies, or maybe both. Please also tell me, if you figured out another issue that I didn´t think of now.