Add test around /etc/my.cnf Preflight

test/boxen_preflight_etc_my_cnf_test.rb

@@ -0,0 +1,10 @@
+require 'boxen/test'
+require 'boxen/preflight/etc_my_cnf'
+
+class BoxenPreflightEtcMyCnfTest < Boxen::Test
+  def test_file_check
+    preflight = Boxen::Preflight::EtcMyCnf.new(mock('config'))
+    File.expects(:file?).with("/etc/my.cnf").returns(false)
+    assert preflight.ok?
+  end
+end