If CleanEveryN fails, such as on fixture teardown, the failure is reported in the test that preceded it rather than in the hook because CleanEveryN is not considered an actual test. This makes finding errors in the logs more difficult. Example:
https://evergreen.mongodb.com/task/mongodb_mongo_master_enterprise_rhel_62_64_bit_jsCore_small_oplog_rs_initsync_956103c27c7f17b850e2cde2738a0eb1f46bcffb_16_10_07_15_00_36