Negative stub test

      it "should fail an invalid file path" do
        File.stubs(:exists?).with('/tmp/nonexistent').returns(:false)
        expect { described_class.new(:domainname => 'domain', :passwordfile => '/tmp/nonexistent') }.to raise_error(Puppet::Error, /does not exist/)
      end

--
  1) Puppet::Type::Domain when validating values for passwordfile should fail an invalid file path
     Failure/Error: expect { described_class.new(:domainname => 'domain', :passwordfile => '/tmp/nonexistent') }.to raise_error(Puppet::Error, /does not exist/)
       expected Puppet::Error with message matching /does not exist/ but nothing was raised
     # ./spec/unit/puppet/type/domain_spec.rb:132:in `block (4 levels) in <top (required)>'