Add or document tests for:
- SpecialSimilarEditors->__construct
- SpecialSimilarEditors->execute
- SpecialSimilarEditors->onSubmit
- SpecialSimilarEditors->onSuccess
- ResultsFormatter->formatRowProperty
See:
https://doc.wikimedia.org/cover-extensions/SimilarEditors/SpecialSimilarEditors.php.html
https://doc.wikimedia.org/cover-extensions/SimilarEditors/ResultsFormatter.php.html