Check that both '/help' and '/help/' URLs have the same behaviour

The links in the help page may be modified. This new test checks that
URLs in this page are absolute and do not depend on the presence of a
trailing slash in the URL.
Signed-off-by: David Wagner <david@marvid.fr>

spec/features/help_pages_spec.rb

@@ -10,4 +10,28 @@ describe 'Help Pages', feature: true do
       expect(page).to have_content("ssh-keygen -t rsa -C \"#{@user.email}\"")
     end
   end
+
+  describe 'Get the main help page' do
+    shared_examples_for 'help page' do
+      it 'prefixes links correctly' do
+        expect(page).to have_selector('div.documentation-index > ul a[href="/help/api/README.md"]')
+      end
+    end
+
+    context 'without a trailing slash' do
+      before do
+        visit help_path
+      end
+
+      it_behaves_like 'help page'
+    end
+
+    context 'with a trailing slash' do
+      before do
+        visit help_path + '/'
+      end
+
+      it_behaves_like 'help page'
+    end
+  end
 end