fork and tests: making it easier

Executive Summary:  I propose Test::Builder 1.5 makes writing tests using fork
as easy as writing tests using threads is.  Test::Builder will handle the
coordination for you.  Downside: this breaks existing behavior.  Rebutal: if
you're testing with fork your tests are probably broken with Test::Builder 1.5
anyway.

Currently, Test::Builder has little knowledge of forking.  This makes forking
in a test problematic if you expect to run tests in both forks.  As people who
have done it know, it involves a lot of fiddling with Test::Builder internals
and yuck.

Test::SharedFork solves this, but its deeply in bed with Test::Builder and
fixing it for Test::Builder 1.5 is difficult.  Test::TCP depends on
Test::SharedFork.  Plack depends on Test::TCP.  So it's important to make it work.

Turns out its easier to just do it inside Test::Builder 1.5.  The state of the
test is encapsulated in a single object and its a not-so-SMOP to freeze and
restore that between processes.  This is what geistteufel and I were working
on at the QA Hackathon.

So I propose having Test::Builder 1.5 coordinate the state of the test like it
does with threads.  It'll take care of the test counter and all that for you.
 There will be a switch to turn coordination off.  It won't hijack fork or
anything.

Upsides:
* Makes writing tests with forks and doing things in parallel much easier.
* Eliminates a lot of Test::Builder hacking which often relies on
  undocumented behaviors and is difficult to support.

Downsides:
* It breaks existing behavior.
  * ...but tests which fork are probably broken with 1.5 anyway.
* It involves file locking, which introduces filesystem complications
  * ...but it will only trigger when a fork runs a test.
    So most tests will be unaffected.
  * ...maybe it can detect if file locking is hosed and error early?
  * ...file locking will be in the temp directory which is usually
    a sane filesystem.
* You might want to fork and run separate tests.
  * ...but this is less common than forking and wanting coordination
  * ...there will be a switch to turn coordination off.

What do you think?


-- 
Who invented the eponym?