Add failing test case for `preload_associations_lazily` for relation with includes called

[PikachuEXE]

This is actually for a potential bug I found and I don't know how to fix Bug: If #includes is called before #preload_associations_lazily, any association not mentioned in includes will not be loaded in a batch when called

See test case for

it "loads association of association automatically when `includes` called"

[coveralls]

Pull Request Test Coverage Report for Build 299

• 8 of 8 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 95.897%

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Totals
Change from base Build 298:	0.04%
Covered Lines:	748
Relevant Lines:	780

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 295

• 8 of 8 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+3.9%) to 99.732%

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Totals
Change from base Build 293:	3.9%
Covered Lines:	745
Relevant Lines:	747

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💛 - Coveralls

[DmitryTsepelev]

Thank you for catching that! I'll try to dig into it during the next few days

[DmitryTsepelev]

The problem is that when includes is called, Rails loads users association as part of posts relation initialization. It means that when users relation is loaded, preloads_associations_lazily? returns false and context is not created. I wonder if we could somehow detect preloading and check if parent association can be lazily loaded (we could do it in the Preloader, but it only has an access to an Array of Post models, not relation).

I guess we should add this issue to the README for now 🙂

[PikachuEXE]

Let's update the readme for now Not an urgent issue for me (I just swap remove calls to includes)

[DmitryTsepelev]

I've added a line and mentioned this issue, so let's keep it open 🙂

[DmitryTsepelev]

Fixed by #48