One of the advantages of views as objects is that we can unit test them. We can both understand if a specific presentational logic behaves correctly and/or assert the contents of the rendered markup.

For the following example we’re gonna use RSpec for the concise syntax for test doubles.

# spec/web/views/books/show_spec.rb
require_relative '../../../../apps/web/views/books/show'
RSpec.describe Web::Views::Books::Show do
  let(:exposures) { Hash[book: double('book', price: 1.00), current_user: user, params: {}] }
  let(:template)  { Hanami::View::Template.new('apps/web/templates/books/show.html.erb') }
  let(:view)      { Web::Views::Home::Another.new(template, exposures) }
  let(:rendered)  { view.render }
  let(:user)      { double('user', admin?: false) }
  context "price" do
    it "returns formatted price" do
      expect(view.formatted_price).to eq("$1.00")
    end
  end
  context "edit link" do
    it "doesn't show it by default" do
      expect(rendered).to_not match(%(<a href="">edit</a>))
    end
    context "when admin" do
      let(:user) { double('user', admin?: true) }
      it "shows it" do
        expect(rendered).to match(%(<a href="">edit</a>))
      end
    end
  end
end

The first part of the test code above is about book’s formatting price. This presentational logic is verified by asserting the returning value of view.formatted_price.

The remaining code is about permissions related logic: the edit link must be rendered only if the current user is an admin. This is tested by looking at the output of the template.

Asserting presentational logic directly via view’s methods, or indirectly via rendered markup are two EQUIVALENT ways.

Notice that exposures includes an unused params key. While this is not strictly required, we recommend providing it since it’s expected by some standard view helpers (e.g. form helpers).

Let’s have a look at the corresponding production code.

# apps/web/views/books/show.rb
module Web
  module Views
    module Books
      class Show
        include Web::View
        def formatted_price
          "$#{ format_number book.price }"
        end
        def edit_link
          if can_edit_book?
            link_to "Edit", routes.edit_book_path(id: book.id)
          end
        end
        private
        def can_edit_book?
          current_user.admin?
        end
      end
    end
  end
end