There are no shell bindings for subunit v2 streams

[Thomi Richards]

We'd like to be able to generate a subunit result stream from a shell script by calling a 'subunit' executable.

I propose adding a 'subunit-output' ython script. The intended usage would be like this:

# Tell subunit that we're starting a test called 'test.name'
subunit-output start test.name

# Tell subunit that the 'test.name' test passed:
subunit-output pass test.name

# similarly, fail 'test.name':
subunit-output fail test.name

We also want to support attaching testtools content objects to the result stream. I propose:

# Attach a detail containing a short text string to the test result, with a label of 'some.data'
subunit-output attach-text "some.data" "some text goes here"

# Attach a detail containing file:
subunit-attach attach-file "screenshot-01" /path/to/some/file.png

Implementation
==============

It looks like I can instantiate a subunit.v2.StreamResultToBytes and call 'status' with values of 'inprogress', 'passed', 'failed' etc to start, pass and fail the tests, as well as attaching details.

I think this should be a single python file named 'filters/subunit-output' (it's not really a filter, but that's where all the other scripts are). This file would just contain "from subunit import output_main; output_main()'.

Testing
======

There's not a lot to test here:
 * The command line parser works as expected (i.e.- raises helpful error messages when the wrong number of parameters are given, for e.g.)
 * Some system tests that call the filter executable with various parameters and ensure that the resulting output can be read in by the subunit module, and the results are all as expected.

Happy to get feedback on this before I start hacking!

[Robert Collins (lifeless)]

So this sounds broadly fine.

A few constraints:
 - must not emit anything on stdout other than the requested packet
 - should export all the functionality of StreamResultToBytes (though not necessarily in one landing)

[Thomi Richards (thomir-deactivatedaccount)]

Ack on those constraints.

[Jelmer Vernooij (jelmer)]

FWIW this is a requirement for Samba moving over to subunitv2 as well.