ActiveRecord association array doesn't behave like a normal array

I have created a failing test in rails/activerecord/test/cases/associations/has_many_through_associations_test.rb

def test_include_method_in_association_through_should_return_true_for_instance_added_by_pushing

person = Person.new
post = Post.new
person.posts.push(post)
assert person.posts.include?(post)

end

I'll try to fix it. Please confirm that it is a bug.

(from [10fa49bc1a25bd2cd25f211e2d8b1771beb58e21]) include_in_memory? should check against @target list in case of new records. [#6257 ActiveRecord association array doesn't behave like a normal array state:resolved] https://github.com/rails/rails/commit/10fa49bc1a25bd2cd25f211e2d8b1...