-*- org *-

<2017-12-11 mån>

A "fixture" is a setup of something, togheter with cleanup behaviour.

The cleanup is performed only if the setup has been performed successfully.

What matters is that setup and cleanup is specified as a single declaration,
and the cleanup is only performed if the setup has been performed successfully.

Exactly has [setup] and [cleanup], and a fixture can be defined in terms of
instructions in [setup] with corresponding instructions in [cleanup].

* Problem

One scenario is problematic, regarding fixtures:
 1. An instruction in [setup] fails, so that the setup of the fixture F
    is never performed.
 2. Execution continues with [cleanup], and the cleanup of the fixture F
    is performed.

The problem is that the cleanup of the fixture may be performed without
the setup having taken place.

* Solution

The solution is to introduce a "fixture" functionality/instruction, that
defines both setup and cleanup, and whos cleanup is performed only if
the setup has been peformed successfully.

The fixture setup and cleanup is defined in terms of an external program.
It is given either "setup" or "cleanup" as the first argument, to
specify the action it should perform.

It is specified in [setup] only:

----------------------------------------
[setup]

fixture my-fixture-program arg1 arg2
========================================

This is equivalent to:

----------------------------------------
[setup]

run my-fixture-program "setup" arg1 arg2

...

[cleanup]

run my-fixture-program "cleanup" arg1 arg2
========================================

And
 - cleanup is not performed for a fixture whos setup has not been performed
 - cleanup is not performed for a fixture whos setup failed

* Implementation

** New feature of the execution environment

An instruction in [setup] may specify behaviour/instructions that
are executed in [cleanup]

** New instruction in [setup]

----------------------------------------
fixture PROGRAM [ARGUMENT]...
----------------------------------------

It is defined by
 1. run PROGRAM "setup" [ARGUMENT]...
 2. If (1) is successful, the following is added to be executed in [cleanup]:
    run PROGRAM "cleanup" [ARGUMENT]...

** Questions

Should fixture cleanup:s be executed before or after instructions in [cleanup]?
