[389-devel] Proof of concept: mocking DS in lib389

[Jan Rusnacko]

On 10/29/2013 03:30 PM, thierry bordaz wrote:
> On 10/29/2013 02:18 PM, Jan Rusnacko wrote:
>> Hello Thierry,
>>
>> I am not rewriting ldapadd,...  methods of "real" DS class, I am in fact
>> creating MockDS class with custom ldapadd,... methods, _just_ like you suggest :)
>>
>> Furthermore, you can view it as a subclass of "real_ds" - even though it is not
>> a proper Python subclass, it inherits all functions from repl module just like
>> "real_ds" would (again through ModuleProxy mechanism). So, methods that are
>> defined in repl are the same for "real_ds" class and for MockDS class, but
>> ldap.. methods are different. So, basically exactly what you suggest :)
> 
> Hi Jan,
> 
>     Sorry my question was not clear. For example an other approach could be
> 
>         Class DSInstance (object):
>             def __init__(self):
>                 ...
>           
>             def ldapadd_r(self, input):
>                 # real call to pythonldap.add_s
> 
>         Class MockDSInstance(DSInstance):
>             def __init__(self):
>                 ...
> 
>             def ldapadd_r(self, input):
>                 input = input.strip()
>                 entry = dict(e.strip().split(': ') for e in input.split('\n'))
>                 self.dit[entry['dn']] = entry
> 
> 
>            
>     My understanding is that both approach would allow us to call inherited
>     methods, just ldap method are different.
>     What are the advantages of the approach you described compare to the one above ?
Oh, ok. Not sure what would be advantage/disadvantage. Result of both approaches
is basically the same ... We could do it this way too.
> 
> best regards
> thierry
>>
>> Code of the whole class along with all methods is in file
>> tests/test_dsmodules/conftest.py line 7.
>>
>> Thank you,
>> Jan
>>
>> On 10/28/2013 12:02 PM, thierry bordaz wrote:
>>> Hi Jan,
>>>
>>>     That is very impressive POC, far above my skill in python. Thanks for
>>>     sharing this.
>>>     I have a novice question.
>>>     This implementation overwrites the basic ldapadd,ldapsearch... function of
>>>     the "real" DS.
>>>     An other approach is to write a 'mock_ds' class being a subclass of
>>>     'real_ds' and to overwrite the ldapadd,ldapsearch in mock_ds class (to store
>>>     data into a dict). What would be the advantages of your approach ?
>>>
>>> best regards
>>> thierry
>>>
>>> On 10/25/2013 09:36 PM, Jan Rusnacko wrote:
>>>> Hello Roberto and Thierry,
>>>>
>>>> as I promised, I am sending you a proof-of-concept code that demonstrates, how
>>>> we can mock DS in unit tests for library function (see attachment). You can run
>>>> tests just by executing py.test in tests directory.
>>>>
>>>> Only 3 files are of interest here:
>>>>
>>>> lib389/dsmodules/repl.py - this is a Python module with functions - they expect
>>>> DS instance as the first argument. Since they are functions, not methods, I can
>>>> just mock DS and pass that fake one as the first argument to them in unit tests.
>>>>
>>>> tests/test_dsmodules/conftest.py - this file contains definition of mock DS
>>>> class along with py.test fixture, that returns it.
>>>>
>>>> tests/test_dsmodules/test_repl.py - this contains unit tests for functions from
>>>> repl.py.
>>>>
>>>> What I do is quite simple - I override ldapadd, ldapdelete .. methods of mock DS
>>>> class, so that instead of sending command to real DS instance, they just store
>>>> the data in 'dit' dictionary (which represents content stored in DS). This way,
>>>> I can check that when I call e.g. function enable_changelog(..), in the end DS
>>>> will have correct changelog entry.
>>>>
>>>> To put it very bluntly - enable_changelog(..) function just adds correct
>>>> changelog entry to whatever is passed to it as the first argument. In unit
>>>> tests, it is mock DS, otherwise it would be real DS class that sends real ldap
>>>> commands to real DS instance behind.
>>>>
>>>> Now I can successfully test that enable_changelog really works, without going
>>>> into trouble defining DSInstance or ldap calls at all. Also, I believe this
>>>> approach would work for 95% of all functions in lib389. Another benefit is that
>>>> unit tests are much faster, than on real DS instance.
>>>>
>>>> Sidenote: even though everything is defined in separate namespace of 'repl'
>>>> module as function, in runtime they can be used as normal methods of class
>>>> DSInstance. That is handled by DSModuleProxy. We already went through this, but
>>>> not with Roberto.
>>>>
>>>> Hopefully, now with some code in our hands, we will be able to understand each
>>>> other on this 'mocking' issue and come to conclusions more quickly.
>>>>
>>>> Let me know what you think.
>>>>
>>>> Thank you,
>>>> Jan
>