[Rpm-maint] [rpm-software-management/rpm] RFE: Standardize on OCI images for test-suite, even locally (Issue #2643)

[Michal Domonkos]

> Keep in mind, we need a way to run it directly on the host, because all this fanciness you're talking about doesn't exist on non-Linux platforms. In particular, I would like to be able to run the test suite for RPM on macOS still. 😅

In essence, what the test-suite needs is a filesystem tree that contains an installation of RPM to test and its runtime dependencies (i.e. a `make install` as root in a development VM would do just fine), and a way to quickly make writable copies (e.g. copy-on-write snapshots) of that tree. Then, a plain chroot into those snapshots could be used to isolate the individual tests.

None of this is inherently Linux specific, however to make it reasonably fast and efficient, you need something like OverlayFS which is currently only available on Linux (and [reportedly](https://github.com/rpm-software-management/rpm/pull/2559#issuecomment-1633335921) on some BSDs through fuse-overlayfs but that's likely slower than a native kernel implementation).

And then, instead of chroot, we *want* to (and *do*) make use of containers in our tests, now that we've freed ourselves from fakechroot. They offer much more possibilities, including proper uid/gid mapping for file ownership testing, unsharing more than just the filesystem namespace, etc.

One way to make the test-suite POSIX compatible would be to identify tests that *require* a proper container and disable those on platforms that don't have containers. There, chroot could be used instead. But I'm not sure if we really want to go in that direction.

Even then, while chroot is available on most UNIX platforms, OverlayFS-like functionality is not, or varies greatly among the systems (APFS on macOS comes close perhaps) and would need special handling. This really is not something we (the core development team at Red Hat) have the resources and/or expertise to cover. We rely on the community to do this work.

One thing that's *not* mandatory, though, is rootless operation. We can always just assume that the test-suite is run in a development/throwaway VM. That's one less thing to worry about when it comes to supporting non-Linux systems.

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