Test If An Instance Variable Was Assigned

When testing Rails controller actions, you'll often be making assertions about the response to your test request. You may also want to assert about the instance variables being set, as those are headed for your view layer.

For instance, if an instance variable @metadata is supposed to be set in a #show controller action, you can assert that it is with RSpec's assigns:

describe "when given valid params" do
  it "sets the metadata" do
    get :show, params: valid_params

    expect(assigns(:metadata)).to match(
      identifier: "abc123",
      session_id: "fe98f08c-bf2f-4749-9f81-071d9cc7720e",
    )
  end
end

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