By adding this option indirection, a test can declare all by itself
that it needs a custom nixpkgs. This is a more convenient way of
going about this when the caller of the test framework receives a
`node.pkgs` unconditionally.
Provide a window during which both solutions are valid without
warnings, in order to fight warning fatigue, and not to push 3rd
party repo maintainers to add unnecessary compat code.
This is a decomposition of the testing-python.nix and build-vms.nix
files into modules.
By refactoring the glue, we accomplish the following:
- NixOS tests can now use `imports` and other module system features.
- Network-wide test setup can now be reusable; example:
- A setup with all VMs configured to use a DNS server
- Split long, slow tests into multiple tests that import a
common module that has most of the setup.
- Type checking for the test arguments
- (TBD) "generated" options reference docs
- Aspects that had to be wired through all the glue are now in their
own files.
- Chief example: interactive.nix.
- Also: network.nix
In rewriting this, I've generally stuck as close as possible to the
existing code; copying pieces of logic and rewiring them, without
changing the logic itself.
I've made two exceptions to this rule
- Introduction of `extraDriverArgs` instead of hardcoded
interactivity logic.
- Incorporation of https://github.com/NixOS/nixpkgs/pull/144110
in testScript.nix.
I might revert the latter and split it into a new commit.
