- Test description language (testscript) [feature]

Requirements
============

* Multiple testscript files (to group related test)

* Run multiple tests

* Specify exit status (optional, expect 0 by default).

* Run pre/post test actions (setups/teardowns, e.g., database schema creation).

* Test input (optional)

* Test stdout output (to compare to, optional)

* Test stderr output (to compare to, optional)

* Test description

* Create (and automatically clean up) input files

? Variable expansion, looked up on target in buildfile

* Ability to pass arguments from build files (how for multiple scripts?)
  Could use $0, $1, $* if have variable expansion.

Questions
=========

* What is the testcript attached at the buildfile level? An executable? What
  if the test is not for executable. I guess we always have the directory
  target.

  We could reuse the test variable to specify (list of) scripts:

  exe{hello}: test = test1 test2

* Do we want a notion of multi-command test (e.g., with pre/post commands)?
  Maybe {}? Will need it not to clean up output files too early.

Notes
=====

* If expected exist status is not 0, then probably makes sense to suppress
  stderr output if there is no comparison.

Syntax
======

The goal is to be as concise as possible at least for the common cases.

$0 World       # hello World, 0 exit expected
$0 "John Doe"  # hello "John Doe"
$0 == 1        # hello, 1 exit expected
$0 != 0        # hello, non-0 exit expected

$0 World >>EOO
Hello, World!
EOO

$0 World >"Hello, World!"

$0 2>>EOE
Usage: $0 <name>
EOE

$0 --trace <<EOI >>EOO 2>>EOE # The data should appear in the order specified.
World
EOI
Hello, World!
EOO
13 characters written
EOE

~ Built in cat command with auto-cleanup? To create files for tests, etc.

~ Output file redirects should be relative to out_base. Input? Could actually
  track created out files and use that if exists, and src otherwise. What if
  the test create a file without a redirect? Will need to "register" it
  somehow for auto-cleanup. Maybe &<file>?

~ Will there be a way to combine stderr and stdout, could be useful sometimes
  (e.g., order of output relative to diagnostics). 2>& syntax?

~ Do we support command piping?

~ What if we actually do want the output to go to a file, e.g., for a second
  command to act on it? Maybe keep shell syntax since familiar?  Or reverse it
  (> - inline, >> - multiline, >>> to file). Simplest thing is the shortest, I
  like it.

~ $0 is target path (works out in case of a directory, but will be out).

~ #-comment (also for mid-line)

~ quoting & escaping (need to think and specify). Would be nice to avoid shell
  madness. Perhaps only support escaping only inside quoted strings).

~ If we support variable expansion inside "here doc", what if we need to
  specify literal '$'? Perhaps treat heredoc as a kind of string? Maybe only
  do effective escaping? Otherwise will have to escape backslashes...

~ Will probably need to support both $foo and $(foo) syntax. Will need to
  replicate var name lexing mode form build2. Perhaps use it to avoid
  duplication?

~ line continuation with \

~ == !=