```ruby
# frozen_string_literal: true

RSpec.shared_examples_for "auditable" do
  let(:model) { described_class }
  let(:model_name) { model.name.underscore.to_sym }

  describe "before validation" do
    let(:current_user) { build_stubbed(:user, id: 1) }
    let(:existing_user) { build_stubbed(:user, id: 2) }

    it "adds the current user id to created_by and updated_by" do
      allow(User).to receive(:current).and_return(current_user)
      resource = build(model_name, created_by: nil, updated_by: nil)
      resource.valid?
      expect(resource.created_by).to eq(current_user.id)
    end

    it "does not change created_by or updated_by if they already exist" do
      allow(User).to receive(:current).and_return(current_user)
      resource = build(model_name, created_by: existing_user.id, updated_by: existing_user.id)
      resource.valid?
      expect(resource.created_by).to eq(existing_user.id)
    end

    it "does not change created_by or updated_by if User.current is not available" do
      allow(User).to receive(:current).and_return(nil)
      resource = build(model_name, created_by: nil, updated_by: nil)
      resource.valid?
      expect(resource.created_by).to eq(nil)
    end
  end
end
```

Update spec to avoid name collisions
user
```ruby
# frozen_string_literal: true

RSpec.shared_examples_for "auditable" do
  let(:model) { described_class }
  let(:model_name) { model.name.underscore.to_sym }

  describe "before validation" do
    let(:current_user) { build_stubbed(:user, id: 1) }
    let(:existing_user) { build_stubbed(:user, id: 2) }

    it "adds the current user id to created_by and updated_by" do
      allow(User).to receive(:current).and_return(current_user)
      resource = build_stubbed(model_name, created_by: nil, updated_by: nil)
      resource.validate
      expect(resource.created_by).to eq(current_user.id)
    end

    it "does not change created_by or updated_by if they already exist" do
      allow(User).to receive(:current).and_return(current_user)
      resource = build_stubbed(model_name, created_by: existing_user.id, updated_by: existing_user.id)
      resource.validate
      expect(resource.created_by).to eq(existing_user.id)
    end

    it "does not change created_by or updated_by if User.current is not available" do
      allow(User).to receive(:current).and_return(nil)
      resource = build_stubbed(model_name, created_by: nil, updated_by: nil)
      resource.validate
      expect(resource.created_by).to eq(nil)
    end
  end
end
```
assistant