Add specs for endpoint meant to be accelerated by workhorse

app/views/projects/artifacts/_tree_file.html.haml

@@ -7,5 +7,5 @@
     = number_to_human_size(file.metadata[:size], precision: 2)
   %td
     = link_to file_namespace_project_build_artifacts_path(path: file.path),
-      class: 'btn btn-xs btn-default' do
+      class: 'btn btn-xs btn-default artifact-download' do
       = icon('download')

features/project/builds.feature

@@ -48,3 +48,11 @@ Feature: Project Builds
     And I click artifacts browse button
     And I navigate to parent directory of directory with invalid name
     Then I should not see directory with invalid name on the list
+
+  Scenario: I download a single file from build artifacts
+    Given recent build has artifacts available
+    And recent build has artifacts metadata available
+    When I visit recent build summary page
+    And I click artifacts browse button
+    And I click download button for a file within build artifacts
+    Then download of a file extracted from build artifacts should start

features/steps/project/builds.rb

@@ -75,4 +75,15 @@ class Spinach::Features::ProjectBuilds < Spinach::FeatureSteps
       expect(page).to have_no_content('non-utf8-dir')
     end
   end
+
+  step 'I click download button for a file within build artifacts' do
+    page.within('.tree-table') { first('.artifact-download').click }
+  end
+
+  step 'download of a file extracted from build artifacts should start' do
+    # this will be accelerated by Workhorse
+    response_json = JSON.parse(page.body, symbolize_names: true)
+    expect(response_json[:archive]).to end_with('build_artifacts.zip')
+    expect(response_json[:path]).to eq Base64.encode64('ci_artifacts.txt')
+  end
 end