Add breaking test for #fetch_route

Author: michael-misshore

spec/lib/critical_path_css/css_fetcher_spec.rb

@@ -1,22 +1,36 @@
 require 'spec_helper'
 
 RSpec.describe 'CssFetcher' do
-  describe '#fetch' do
-    let(:subject) { CriticalPathCss::CssFetcher.new(config) }
-    let(:response) {
-      ['foo','', OpenStruct.new(exitstatus: 0)]
-    }
-    let(:routes) { ['/', '/new_route'] }
-    let(:config) do
-      OpenStruct.new(
-        base_url: 'http://0.0.0.0:9292',
-        css_path: css_path,
-        css_paths: css_paths,
-        penthouse_options: {},
-        routes: routes
-      )
+  let(:subject) { CriticalPathCss::CssFetcher.new(config) }
+  let(:response) { ['foo','', OpenStruct.new(exitstatus: 0)] }
+  let(:routes) { ['/', '/new_route'] }
+  let(:config) do
+    OpenStruct.new(
+      base_url: 'http://0.0.0.0:9292',
+      css_path: css_path,
+      css_paths: css_paths,
+      penthouse_options: {},
+      routes: routes
+    )
+  end
+
+  describe '#fetch_route' do
+    context 'when a single css_path is configured' do
+      let(:css_path) { '/test.css' }
+      let(:css_paths) { [] }
+
+      it 'generates css for the single route' do
+        expect(Open3).to receive(:capture3) do |arg1, arg2, arg3|
+          options = JSON.parse(arg3)
+          expect(options['css']).to eq '/test.css'
+        end.once.and_return(response)
+
+        subject.fetch_route(routes.first)
+      end
     end
+  end
 
+  describe '#fetch' do
     context 'when a single css_path is configured' do
       let(:css_path) { '/test.css' }
       let(:css_paths) { [] }