RSpec: How to pass a "let" variable as a parameter to shared examples

Question

The relevant fragment of spec looks like that:

let(:one_place) { create(:place) }
let(:other_place) { create(:place) }
let(:data) { "saved data" }

shared_examples "saves data to right place" do |right_place|
  it { expect(right_place.data).to eq data }
end

context "when something it saves to one place" do
  it_behaves_like "saves data to right place", one_place
end

context "when whatever it saves to other place" do  
  it_behaves_like "saves data to right place", other_place
end

And it would works perfectly with constant parameters, but in this case I receive an error:

one_place is not available on an example group (e.g. a describe or context block). It is only available from within individualexamples (e.g. it blocks) or from constructs that run in the scope of an example (e.g. before, let, etc).

How to pass a lazily created variable to shared examples in such a case?

Answer 1

From the docs, I think you need to put your let statement in a block passed to it_behaves_like:

let(:data) { "saved data" }

shared_examples "saves data to right place" do
  it { expect(right_place.data).to eq data }
end

context "when something it saves to one place" do
  it_behaves_like "saves data to right place" do
    let(:right_place) { create(:place) }
  end
end

context "when whatever it saves to other place" do  
  it_behaves_like "saves data to right place" do
    let(:right_place) { create(:place) }
  end
end

Answer 2

I'd point out that what you're trying to accomplish is unfortunately not possible. It would be desirable because it makes the usage of such variables explicit. The mentioned workaround (define let where you use it_behaves_like) works but I find shared examples written like that to be confusing.

I use a shared example to make required variables explicit in shared examples:

RSpec.shared_examples "requires variables" do |variable_names|
  it "(shared example requires `#{variable_names}` to be set)" do
    variable_names = variable_names.kind_of?(Array) ? variable_names : [variable_names]
    temp_config = RSpec::Expectations.configuration.on_potential_false_positives
    RSpec::Expectations.configuration.on_potential_false_positives = :nothing

    variable_names.each do |variable_name|
      expect { send(variable_name) }.not_to(
        raise_error(NameError), "The following variables must be set to use this shared example: #{variable_names}"
      )
    end

    RSpec::Expectations.configuration.on_potential_false_positives = temp_config
  end
end

Use it like this:

RSpec.shared_examples "saves data to right place" do
  include_examples "requires variables", :right_place

  # ...
end

context "..." do
  it_behaves_like "saves data to right place" do
    let(:right_place) { "" }
  end
end