extensions/filters/common/fault coverage

Hello,
The Envoy project has recently started collecting per-extension coverage. You have been tagged with this issue as you are a co-owner of an extension, extensions/filters/common/fault, which is below the 96.6 percent coverage mark.
Could you please take a look at coverage results (https://storage.googleapis.com/envoy-postsubmit/master/coverage/index.html) and add more tests when you get a chance? Once this is done you should be able to remove your extension from the exempt extensions in [test/per_file_coverage.sh](https://github.com/envoyproxy/envoy/blob/master/test/per_file_coverage.sh)
Thanks!