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

[Jan Rusnacko]

On 10/25/2013 11:00 PM, Rich Megginson wrote:
> On 10/25/2013 01:36 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.
> def test_add_repl_manager(fake_ds_inst_with_repl):
>     ds_inst = fake_ds_inst_with_repl
>     ds_inst.repl.add_repl_manager("cn=replication manager, cn=config", "Secret123")
>     assert ds_inst.dit["cn=replication manager, cn=config"]["userPassword"] ==
> "Secret123"
>     assert ds_inst.dit["cn=replication manager, cn=config"]["nsIdleTimeout"] == "0"
>     assert ds_inst.dit["cn=replication manager, cn=config"]["cn"] ==
> "replication manager"
> 
> If you are using a real directory server instance, doing add_repl_manager() is
> going to make a real LDAP ADD request, right?
Correct. If you pass DS with real ldapadd method that makes real reqests, its
going to use that.
> Will it still update the ds_inst.dit dict? 
ds_inst.dit is updated in mocked ldapadd. So in real ldapadd, no.
> Wouldn't you have to do a real LDAP Search request to get the
> actual values?
Yes, correct. ds_inst.dit[] .. call is specific to mocked DS.

But you are right - I could add fake ldapsearch method, that would return
entries from 'dit' dictionary and use that to retrieve entries from mocked DS.
> 
>>
>> 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
>