I'm not sure this is needed anymore, the [spec_helper.rb](https://github.com/puppetlabs/puppet/blob/master/spec/spec_helper.rb#L119) executes [test_helper.rb](https://github.com/puppetlabs/puppet/blob/master/lib/puppet/test/test_helper.rb#L93), which [clears the settings](https://github.com/puppetlabs/puppet/blob/master/lib/puppet/settings.rb#L1174). But it may not be exactly the same as calling `clearused`?