stub out file system for CLI tests

prevents creating real files and folders

spec/cli_spec.rb

@@ -2,8 +2,21 @@
 require_relative '../lib/sandi_meter/cli'
 
 describe SandiMeter::CLI do
+  include FakeFS::SpecHelpers
+
   let(:cli) { SandiMeter::CLI }
+  let(:gem_root) { File.expand_path('../', File.dirname(__FILE__)) }
 
+  before do
+    FakeFS.activate!
+
+    FakeFS::FileSystem.clone(gem_root)
+  end
+
+  after do
+    FakeFS.deactivate!
+  end
+
   describe '#execute' do
     before do 
       @original_argv = ARGV