Check for both backup files

spec/lib/backup/manager_spec.rb

@@ -197,7 +197,7 @@ describe Backup::Manager do
       it 'prints the list of available backups' do
         expect { subject.unpack }.to raise_error SystemExit
         expect(progress).to have_received(:puts)
-          .with(a_string_matching('1451606400_2016_01_01_1.2.3'))
+          .with(a_string_matching('1451606400_2016_01_01_1.2.3\n 1451520000_2015_12_31'))
       end
       it 'fails the operation and prints an error' do