Add spec for AsciicastSnapshotter

spec/workers/snapshot_worker_spec.rb

@@ -0,0 +1,17 @@
+require 'spec_helper'
+
+describe SnapshotWorker do
+  let(:worker) { SnapshotWorker.new }
+
+  describe '#perform' do
+    let(:snapshotter) { double('snapshotter', :run => nil) }
+
+    it 'calls #run on AsciicastSnapshotter' do
+      allow(AsciicastSnapshotter).to receive(:new).with(123) { snapshotter }
+
+      worker.perform(123)
+
+      expect(snapshotter).to have_received(:run).with(no_args())
+    end
+  end
+end