Documentation for ResourceSerializer with includes is incorrect

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• Problem/bug report.
• Feature request.
• Request for support. Note: Please try to avoid submitting issues for support requests. Use Gitter instead.

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• I've searched for an existing issue.
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• The feature I'm asking for is compliant with the JSON:API spec.

Description

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Bug reports:

The documentation says that ResourceSerailizer should be able to include resources by doing something like this:

post = Post.find(1)

JSONAPI::ResourceSerializer.new(PostResource,
  include: ['comments'],
).serialize_to_hash(PostResource.new(post, nil))

But when I do this I don't get an included section in the serialized output.

Additionally I don't find any tests in the test suite that demonstrate the documented way of doing it, but I find several tests that seem to achieve includes via much more verbose and laborious methods.

Am I missing something?

Start with the v0.10 serializer guide's include section and compare its example with test/unit/serializer/serializer_test.rb around lines 205-226. Reproduce the documented ResourceSerializer call, then determine whether the documentation or serializer behavior is incorrect. Done means the documented include workflow is accurate and covered by a focused test.