A virtual KWin has no output to draw on, so every test about pixels, and later
about the pointer, needs a real session. The `session` node is the headless node
plus a login: plasma-login-manager logs the test user in by itself, the way
nixpkgs' own `plasma6` test does, and Plasma draws on the machine's display. The
choice of login manager is made in `nodes/session.nix` and nowhere else, and the
file says how to switch to sddm.
The node adds no display device. The test driver gives every aarch64 guest one
virtio-gpu and takes screenshots of it; a second device is a second KWin output
that screenshots never show, which is what a first attempt did (a blank 1280x800
console).
`Kde.session` attaches to the session once the desktop is up: the shell is
running, the user manager knows the Wayland display, and the splash screen has
gone. The display is read from the user manager because plasma-login-manager's
greeter has its own KWin and takes `wayland-0`, and the user's session gets
`wayland-1`. The splash condition is there because KSplash has over a thousand
colors on it, so a "not blank" check passed on the splash screen. NixOS wraps
programs, which is why processes are found by their command lines: `pgrep -x
plasmashell` never matches `.plasmashell-wrapped`, and an exact match for the
splash would have passed because nothing matched. `Kde.shot` returns a
screenshot as a Pillow image.
`vm-render-smoke` is the first slow suite: it starts a session, opens a
terminal, and checks the middle of the window is dark and that the desktop
behind it has thousands of colors. On aarch64 under HVF five runs gave the same
screenshot, with the desktop up after 34 seconds. docs/dev/vm-tests.md describes
the node and the two traps.
The unit tests run against a fake desktop and cannot say whether KWin does what
the daemon asks. This adds the other half: NixOS machines with Plasma in them, a
real KWin, and a Python library to drive it.
Every directory under `nix/tests/vm/suites` is a test. The generator lists the
directory, so a new suite appears as `checks.<system>.vm-NAME` on Linux and as
`legacyPackages.<system>.vm.NAME` everywhere, with no edit to the flake. A suite
names its tier and its node and has a `test.py`;
`legacyPackages.<system>.vmTiers` lists the names of each tier as JSON for the
CI matrix, `vmGuests` the guests to build on a Linux builder, and `vmTcg` the
same suites for a machine with no KVM. `scale` multiplies every wait: 1 for KVM,
1.5 for HVF, 8 for TCG.
The headless node runs `kwin_wayland --virtual` as user units of a lingering
user, one pair of units per session (`session-bus@NAME`, `kwin-virtual@NAME`),
so a test can run several sessions with their own bus and socket. A virtual KWin
has no output to draw on, so anything that needs pixels or a pointer needs the
session node.
The library, `komorebi_vm`, has `Checks` (counted checks that fail once, at the
end) and `Kde` (start a session, run clients and tools inside it, read windows
through kdotool, poll with `wait_for`). It depends on a small `Machine` protocol
rather than on the test driver. The `vm-lib` check runs its unit tests against a
fake machine, with ruff and ty. The driver type checks each `test.py` with ty,
which is how a protocol that did not match `QemuMachine.execute` was caught.
`vm-kwin` starts a KWin with two outputs, spawns a foot window, reads it back,
starts a second session and checks that it cannot see the first.
On a Mac the guest is built on a Linux builder and the driver run directly,
because the macOS nix sandbox cannot give QEMU the hypervisor: `scripts/vm-mac`,
`just vm NAME`. docs/dev/vm-tests.md covers this, adding a test, and the
builder.
LGUG2Z