CachingUtilitiesTest.py: Add test for local build

[harshhx17]

This adds test to CachingUtilitiesTest.py for the code in
CachingUtilities.py which runs when coala is run for the first
time on the project

Fixes #5206

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[harshhx17]

Here are the new local build logs
https://gist.github.com/harshhx17/eef0dc45b04dec9a3bca931e8f97e72c

[alphadose]

Your commit message needs work.
This adds test... ->
Add test for CachingUtilities when coala is run for the first time on the project.

[harshhx17]

@Makman2 can you please review it 😄

[adtac]

This does not solve the problem. It just patches the symptom.

To properly solve this, create a tearDown that deletes all side effects from the tests after the tests are done.

[adtac]

By this, I mean to say remove all keys related to tests from the pickle after the tests are done.

[jayvdb]

@harshhx17 replied at #5216 (comment)

[jayvdb]

Replying to ^ , this isnt about what you have done or not done.

@adtac is asking you to re-create the scenario which this if is supposed to address.

Your code does force the use of this if branch, which does achieve 100% coverage, but it doesnt reproduce the scenario, so the objective of 100% coverage isnt obtained.

The line settings_hash_db = pickle_load(None, 'settings_hash_db', {}) will already return {}, so you dont need to mock pickle_load. You could mock something quite a bit deeper to cause {} to be returned. That may not make @adtac happy, but at least you are more closely recreating the scenario.

@adtac is saying you should use setUp and tearDown to create the scenario, e.g. create a backup of the setting cache, remove the settings for this directory, and then restore the settings again after the test is completed.

As it is an invasive test process, I suggest putting it into its own test class.

[harshhx17]

I will look into it 😄

[harshhx17]

@adtac
imo, Since I have not created any class variable, I do not think the variables related to the pickle tests will exist outside the scope of the patch call...
However, if i had used a patcher(and mocked CachingUtilities.pickle_load as self.mocked_pickle_load) in the setup(which would mock the pickle_loadd to all the tests), I would need to add that to the teardown so that it doesnot effect other tests....[which i have not done as it is not required by all the tests]