This is just a prototype to gather some feedback in our ongoing research
on integration testing of Terraform modules. The hope is that by having a
command integrated into Terraform itself it'll be easier for interested
module authors to give it a try, and also easier for us to iterate quickly
based on feedback without having to coordinate across multiple codebases.
Everything about this is subject to change even in future patch releases.
Since it's a CLI command rather than a configuration language feature it's
not using the language experiments mechanism, but generates a warning
similar to the one language experiments generate in order to be clear that
backward compatibility is not guaranteed.
As part of ongoing research into Terraform testing we'd like to use an
experimental feature to validate our current understanding that expressing
tests as part of the Terraform language, as opposed to in some other
language run alongside, is a good and viable way to write practical
module integration tests.
This initial experimental incarnation of that idea is implemented as a
provider, just because that's an easier extension point for research
purposes than a first-class language feature would be. Whether this would
ultimately emerge as a provider similar to this or as custom language
constructs will be a matter for future research, if this first
experiment confirms that tests written in the Terraform language are the
best direction to take.
The previous incarnation of this experiment was an externally-developed
provider apparentlymart/testing, listed on the Terraform Registry. That
helped with showing that there are some useful tests that we can write
in the Terraform language, but integrating such a provider into Terraform
will allow us to make use of it in the also-experimental "terraform test"
command, which will follow in subsequent commits, to see how this might
fit into a development workflow.
Martin Atkins