adds acceptance test for ruby file: "" syntax

spec/acceptance/appraisals_file_bundler_dsl_compatibility_spec.rb

@@ -149,4 +149,33 @@
       gemspec :path => "../sitepress"
     Gemfile
   end
+
+  it 'supports ruby file: ".ruby-version" DSL' do
+    build_gemfile <<-Gemfile
+      source 'https://rubygems.org'
+
+      ruby RUBY_VERSION
+
+      gem 'appraisal', :path => #{PROJECT_ROOT.inspect}
+    Gemfile
+
+    build_appraisal_file <<-Appraisals
+      appraise 'ruby-version' do
+        ruby file: ".ruby-version"
+      end
+    Appraisals
+
+    run 'bundle install --local'
+    run 'appraisal generate'
+
+    expect(content_of 'gemfiles/ruby_version.gemfile').to eq <<-Gemfile.strip_heredoc
+      # This file was generated by Appraisal
+
+      source "https://rubygems.org"
+
+      ruby({:file=>".ruby-version"})
+
+      gem "appraisal", :path => #{PROJECT_ROOT.inspect}
+    Gemfile
+  end
 end