SERVER-83076 introduced a MockAppender class which audits to an in-memory buffer.  This mock appender could potentially speed up the audit jstest suite by avoiding repeated disk reads from the AuditSpooler JS class.

This will likely necessitate expanding the MockAppender from only last-line to a FIFO buffer of N lines (N being configurable) and a counter.  A test-only command would be required to provide a means for querying these count/buffer values.