Mongoid test suite historically set individual option values as needed in each test. Sometimes these options weren't reset back to defaults, which could affect subsequent tests. When the options were reset, they sometimes were reset to what was the default at the time the test was written, not to the active runtime value, which would yield wrong behavior if the default was changed (as happened for 8.0).

All tests which need specific local configuration option values should use config_override to correctly gain those values for the duration of the tests.