Fix RSpec/DescribedClass false positive for Data objects

[bkuhlmann]

Expected behavior

Hello. 👋 I'm running into a situation where Struct and Data behavior are not consistent when including a module. For a Struct, you don't get a RSpec/DescribedClass error but with a Data object, you do.

The reason is that you can't use include described_class as RuboCop tries to tell you because you'll get the following error:

NameError: undefined local variable or method 'described_class' for class #<Class:0x00000001048b2630>

Actual behavior

The best way to see this is when comparing/contrasting behavior between a Struct and Data object. Example:

RSpec.describe Demo do
  let :struct do
    Struct.new(:name, :label) { include Demo }
  end

  let :data do
    Data.define(:name, :label) { include Demo }
  end
end

With a Struct, you won't get a RSpec/DescribedClass error but with Data, you will.

Steps to reproduce the problem

Here's a quick example (albeit contrived) to reproduce the error:

Demo = Module.new

RSpec.describe Demo do
  describe "#initialize" do
    let :implementation do
      Data.define(:name, :label) { include Demo }
    end

    it "answers Data type" do
      expect(implementation[name: "test", label: "Test"]).to be_a(Data)
    end
  end
end

RuboCop RSpec version

1.75.5 (using Parser 3.3.8.0, Prism 1.4.0, rubocop-ast 1.44.1, analyzing as Ruby 3.4, running on ruby 3.4.3) [arm64-darwin24.4.0]
  - rubocop-capybara 2.22.1
  - rubocop-disable_syntax 0.2.0
  - rubocop-packaging 0.6.0
  - rubocop-performance 1.25.0
  - rubocop-thread_safety 0.7.2
  - rubocop-rake 0.7.1
  - rubocop-rspec 3.6.0