Compiling plugins was originally intended to be an idempotent operation.
This however starts to change as we introduce build customisations,
which have the unfortunate side-effect of changing the state of the
plugin directory, leading to conflicts between concurrent compilation
jobs.
Therefore to mitigate this problem, this commit changes how compilation
jobs are processed, by introducing a global compilation queue, and
processing plugins' compilation one-by-one from this queue.
This however makes such requests asynchronous, so test suites that
require plugins to be compiled will now have to wait on their completion
before they can start their tests.
To this effect, we introduce one more convenience function that
processes those errors, and automatically fails the test should one
compilation job fail for any reason.
When building a plugin, we may want some customisation capabilities
beyond changing the version/pre-release/metadata, and instead run
commands or change files on the filesystem.
To do so, we introduce functions under the BuildCustomisation type,
which have two responsabilities: changing the current state of the
plugin's directory, and cleaning up afterwards.
These customisations are passed as parameters to the BuildSimplePlugin
function, and are called one-by-one, deferring their cleanup after the
build process is finished.
A first implementation of such a customisation is added with this
commit, in order to change the version of a module that the plugin
depends on, which we'll use to change the version of the plugin SDK in
order to test how Packer behaves with different versions of the SDK for
a single plugin.
In order for the creation of a temporary directory to install plugins
into to be simpler to understand and use, we change how the directory is
created, cleaned-up, and installs plugins into.
Now, instead of a tuple of a string (path) and a cleanup function, we
return a structure that comprises the test suite, and the temporary
directory, along with methods to handle those steps independently.
When using a PackerCommand, the Run function was made public as a way to
access the contents of an execution.
This was clumsy as it had too many responsabilities, and was not needed
strictly as Assert was performing the executions, as many times as
required.
This could introduce cases in which one run as spent by the caller, then
the remainder were executed through Assert.
Therefore, we change this convention.
Now, run is private to the type, and only through Assert can a command
be executed.
If a test needs access to a command's output, stderr, or error, it can
do so through the Output function, which requires Assert to be called
first.
The lib name for the common components for writing packer_test suites
was not clear, and did not follow the convention established in Packer
core and plugins.
Therefore this commit does two things: first the lib is renamed into
common as to follow this convention, and clearly document which
components are common to all tests.
Also checkers are placed in a subpackage of common, common/check, so
that it is clearer what is meant to be used as checks for a command's
execution status after it's been run, as part of Assert.
