Subunit is a streaming protocol for test results.

There are two major revisions of the protocol. Version 1 was trivially human
readable but had significant defects as far as highly parallel testing was
concerned - it had no room for doing discovery and execution in parallel,
required substantial buffering when multiplexing and was fragile - a corrupt
byte could cause an entire stream to be misparsed. Version 1.1 added
encapsulation of binary streams which mitigated some of the issues but the core
remained.

Version 2 shares many of the good characteristics of Version 1 - it can be
embedded into a regular text stream (e.g. from a build system) and it still
models xUnit style test execution. It also fixes many of the issues with
Version 1 - Version 2 can be multiplexed without excessive buffering (in time
or space), it has a well defined recovery mechanism for dealing with corrupted
streams (e.g. where two processes write to the same stream concurrently, or
where the stream generator suffers a bug).