firmware/docs/testing.md

# Testing: how we know it does not brick

**`qa/` is the suite.** One framework (pytest), two lanes, and a result per
assertion rather than per case script.

```sh
make qa            # both lanes
make qa-static     # seconds, any machine, any clone -- no docker
make qa-replica    # the gates that decide whether a package bricks a printer
```

Selection is pytest's: `-k nginx`, `-m static`, or a single test id.
[qa-migration.md](qa-migration.md) is the design and the history.

## The lanes

| Lane | Needs | What it asks |
|---|---|---|
| `static` | the checkout; the feed for part of it | every shipped script parses and is free of bashisms, every name resolves, the recipe layout holds, and -- when `work/packages` exists -- the `.apk`s are what we mean to ship |
| `replica` | docker + qemu + the firmware | what the printer *does* -- on a machine the real `app_startup.sh` installed the real package onto |

The replica lane needs a built package in `work/out/*.tgz` (`make build`) and
`PRINTER_IMAGE` in `test.env` — that image *is* the replica, and there is no
other way to get one. `test.env.example` carries the published tag; `make
printer-image` builds your own from public firmware. The install is baked into
an image once per package, keyed on the package's md5, so rebuilding gets you
a fresh bake and not yesterday's.

**The static lane is worth running twice**, and CI does. A good part of it
asks what is inside the `.apk` files, and those questions do not fail on a
checkout that has no feed — they return quietly, and the lane reports a pass
having never opened a package. Run it once for the fast parse-and-name
feedback, then again after `make packages`, when the rest of it can bite.

### The replica lane, module by module

| module | asks |
|---|---|
| `test_install.py` | what the machine's own installer produced: the stock boot chain is untouched and still parses, the wrapper is installed and starts the supervisor, every installed script is `sh -n`-clean under the printer's own busybox, klipper and the UI are services in the compiled database, klipper depends on the bring-up, the config include set is wired up, the user's `printer.cfg` survived, and a boot with no stick does not go looking for an update |
| `test_abi.py` | the ABI gate, and the only one there is: every ELF object on the installed filesystem -- ours, the stock tree's and whatever `bin/payload.sh` staged -- is 32-bit little-endian MIPS, and every one the kernel's loader will handle is `nan2008/o32/mips32r2`. Two exemptions, both measured and both narrow: kernel modules are `ET_REL` and have no FP ABI to agree about, and FlashForge ships one inert ARM binary |
| `test_upgrade.py` | an update replaces the whole of `/usr/data/anvil` -- a renamed file leaves no stale twin, and a file nobody shipped goes too -- while HelixScreen's settings are carried across it and `/usr/data/config`, where `printer.cfg` and `moonraker-custom.conf` live, is never touched |
| `test_supervisor.py` | the s6 we cross-compiled: all 13 binaries load on the printer's kernel, and `s6-svwait -U` really waits for readiness rather than returning on the fork |
| `test_boot_screen.py` | the first-boot screen renders on our own CPython 3.13, one screen's worth of correctly packed bytes, and degrades to "no screen" rather than raising when there is no panel |
| `test_web.py` | nginx and moonraker come up under s6, nginx comes back from a kill and stays down after a stop, and moonraker serves on `:7125` on our interpreter |
| `test_s6rc.py` | the boot itself -- the scanner answers, `s6-rc-init` lays the scandir down, a killed daemon comes back |
| `test_mcu_bringup.py` | `ff_mcu_bringup.py` runs on `FF_PYTHON` in the shipped environment and names every port it could not open |

**Eight of `test_s6rc.py`'s twelve cannot pass on a replica**, and that is
hardware, not a bug: there are no `/dev/ttyS4,5,7` and no `/dev/video*`, so
klippy never connects, `camera` times out, and the `ok-all` bundle is
unreachable. See [qa-migration.md](qa-migration.md). Everything else is green.

## `test/` is gone

`test/run-tests.py` went first, and `make test` with it. The 28 host-side unit
tests that outlived it -- `test_startup.py`, `test_tool_transform.py`,
`test_ffscreen.py`, `test_chamber.py`, `test_gcode.py` and the two fixtures
they shared -- are deleted too, along with `make test-py` and the CI step that
ran them. `qa/` is the only suite.

What this costs is worth naming rather than leaving to be discovered. The
replica lane covers the boot screen on the real interpreter
(`qa/replica/test_boot_screen.py`) and the install end to end, but nothing now
checks the tool-frame arithmetic in `ff_toolchange`, the chamber macros'
per-model branching, the stamp discipline in `ff-startup.py`, or the
verification G-code against the macros we ship. Those were host-side unit
tests over our own Python, and they have no replacement.

## The replica is a tool, not a test

`tools/replica/` builds the machine both suites run against, and the build
uses it too -- `bin/payload.sh` assembles the payload by running the printer's
own `apk` inside it. It is not under `test/` because nothing in it is a test:

```
tools/replica/
  printer/                  the replica itself: the Dockerfile, binfmt.sh,
                            assemble.sh, entrypoint.sh, seed-prog.sh, bake.sh
  ffsim/                    the host half -- config loading and the docker
                            plumbing. NOT a test framework; it was one, and
                            what is left of it launches containers
  build-printer-image.sh    bakes the replica image -- fetches the firmware
                            itself, so it needs no stock package on disk
  sim-boot-screen.py        `make boot-screen-sim`
```

`qa/lib/replica.py` drives `tools/replica/printer/` unmodified; it holds a
container open where `ffsim` runs one case script and exits.

## Why the harness is Python

The host half of the harness — the orchestrator and the replica launchers —
was shell until August 2026. It moved to Python for one specific reason, and
it is worth stating because the rule it enforces is the one above.

In the shell suite, "this gate did not run" travelled between processes as the
string `SKIP:` on stdout, and the runner decided by grepping for it:

```sh
if "$@" >"$out" 2>&1; then
    if grep -qE '^[[:space:]]*SKIP:|[0-9]+ skipped' "$out"
    then skip "$name"; else pass "$name"; fi
```

Text on stdout cannot tell you what happened inside a process. A launcher that
had **already failed** would reach the same line by a different road: the file
that sources `config.env` failed to load, so `STOCK_TGZ_*` was never set, so
the launcher concluded there was nothing to test, printed those five
characters and exited 0 — on a machine with docker and the firmware sitting
right there. That is not a hypothetical; it is how five broken launchers
shipped and stayed broken.

What changed:

- **A skip is an exception** (`ffsim.Skip`), not a string. Output cannot
  imitate it, and a gate that fails cannot accidentally claim it was skipped.
- **The repo root is found by searching** upward for `bin/common.sh`, not by
  counting `..` from `$0`. Moving a launcher to a different depth used to
  break it silently; now it cannot.
- **A broken config is not an absent one.** Sourcing a file with a syntax
  error returns non-zero and does *not* stop the shell, so the old code
  carried on with half a config. `ffsim.config` checks each source and names
  the file that failed.
- **pytest results are read from JUnit XML**, not from grepping `N skipped`.
- **The suite calls the gates as functions.** There is no subprocess between a
  gate and the thing counting results, so there is no format to agree on.

The four things that used to be reported as skips and are now failures:
a `config.env` that does not parse, a missing case script, a missing package,
and a missing baseline. A genuinely absent precondition — no docker, no stock
package — is still a skip, because that is still the truth.

## Speed

Almost all of a replica run used to be setup, repeated per test case:

| | per run |
|---|---|
| unpack the 182MB factory image into `/usr/prog` | 22s |
| install the stock package into it, under qemu | 37s |
| **the test itself** (three boots, install, re-install) | ~30s |

`make printer-image` does both of those once, at build time, and publishes the
result. `tools/replica/printer/bake.sh` is the part that cannot be a `docker build`
step — the stock install needs `binfmt_misc` and `chroot`, so it runs in a
privileged container and the result is committed. The md5 of the package that
was installed is recorded in `/usr/prog/.BASELINE`; `entrypoint.sh` reinstalls
only if a run asks for a different one.

A replica now starts in **0.7s** and the whole end-to-end update test takes
**~70s**. That image contains proprietary FlashForge firmware.

There used to be a second way in, and it is where the numbers in that table
came from: `make rootfs` unsquashed `rootfs.squashfs` out of a stock package
into `work/rootfs`, and a thin container mounted it and unpacked the factory
image for `/usr/prog` on every single case. It is gone. Every caller set
`PRINTER_IMAGE` anyway — CI extracted a rootfs on every push and read none of
it — and `make printer-image` builds the image from the same public firmware
without needing a stock package at all, so the slow path was a second route to
the same machine that nothing chose. When the image goes stale, rebuild it.

What takes the time now is real work: two full package builds (the payload is
55MB through `xz`) and two replica runs. If it needs to get faster again,
that is where to look — not in the harness.

## What was dropped, and why

Tests that cannot fail are worse than no tests, because they read as coverage:

- **`test-abi`'s execution half.** It was `qemu "$f" -h || [ $? -lt 126 ]`,
  which accepts nearly every exit status — it could only fail if qemu itself
  was missing. Running the binaries for real is what the replica does.
- **`test-ash`'s `md5sum -s` probe.** It printed "inconclusive" on every path
  and could not fail.
- **The per-file `sh -n` "POSIX" loop in `run-tests.sh`.** `sh` is bash on the
  build image, so it proved nothing that `test-ash` does not prove properly
  with the printer's own busybox. Its bashism grep also flagged `local`, which
  busybox ash supports.
- **`test-install`'s hand-written replay of `app_startup.sh`.** It re-derived
  the glob, `MACHINE` and `PID` with `sed` and then called the installer
  itself — so a mistake in our reading of the boot script could never be
  caught. The replica now runs the boot script itself, and
  `qa/replica/test_install.py` asserts against what it produced.
- **The release workflow's final `sim-install` loop** ignored the exit status
  of every run, so the last gate before publishing could not fail. It stops on
  the first failure now, and it is `REAL_PKG=<pkg> pytest ./qa/replica` per
  model -- 22 named results for each package that ships, where the loop gave
  one exit code it was throwing away.
- **`test-printer-db`, all of it.** It began as a re-implementation of
  PrinterDetector's scoring formula, mirroring `printer_detector.cpp` line for
  line, so a change to the HelixScreen fork's formula left the test passing
  while reality moved. Narrowing it to scoring-independent invariants kept it
  honest but not useful enough to earn its place, and the whole check is gone.
- **The hand-rolled bashism grep in `run-tests.sh`.** It knew five constructs;
  `shellcheck -s dash` knows the whole SC3xxx family and now stands in its
  place. The same pass gave every replica launcher one shared home for the
  docker plumbing — now `tools/replica/ffsim/replica.py` — which also fixed two `make
  test-ash` bugs: it ran without the docker socket (so it always silently
  skipped), and it never read `test.env`, so it ignored `PRINTER_IMAGE` and
  rebuilt the local sim image every run.

- **Eight checks, in one pass, once each had been read properly.** The suite
  had grown to twelve gates and most of them were the weaker copy of a gate
  that survives:
  - `test-abi` had **never asserted anything in CI**. `run-tests.sh` deleted
    `work/modpayload` immediately before it ran and CI set `KLIPPER_FORK=""`,
    so it had no targets on any run, skipped, exited 0 and was printed as
    `ok`. `qa/replica/test_abi.py` now reads the ELF header of every object
    that actually landed, which is the check `test-abi` was aiming at.
  - `test-macros` used `jinja2.Environment()` — the default `{{ }}` syntax.
    The configs contain **no** `{{` at all, only single-brace expressions, so
    it validated `{% %}` block structure and never once looked inside an
    expression. `test_default_delimiters_are_blind` now pins that.
  - `test-ash-conformance` parsed the payload with the printer's busybox;
    `qa/replica/test_install.py` runs `sh -n` over every *installed* script
    with the same qemu'd busybox.
  - `test-model-gate` checked what `bin/verify.sh` §8b/§9 checked and what
    `pack.sh` already refuses to build. Its header claimed it proved the two
    models ship different files; no such check existed in it. `verify.sh` has
    since been retired; the model gate is now enforced where it always
    mattered, by `runFirmwareExe.sh` refusing a foreign package -- which the
    replica lane exercises on every install.
  - `test-base-cfg` compared our `printer.base.cfg` against
    `work/software/.../printer.base.cfg` — which the build overwrote *with our
    own file* before the test read it. It had been diffing our file against
    itself: green on a cold tree, red on a second build, and blind to real
    drift either way. The comparison moved into `bin/unpack.sh`, where a
    pristine stock tree actually exists.
  - `test-applets`' command-word scan only extracted the first word of a
    simple, unprefixed command: `if timeout 5 foo; then` yielded
    `['if','echo','fi']`, so the one failure its docstring named was invisible
    to it. Its allowlist had drifted to nine entries that excused nothing. The
    absolute-path half survives, because `S50wifi`'s binaries sit on a branch
    no simulation reaches.
  - `lint-danger`'s structural greps were satisfiable by comments — the
    comments in `firmwareExe` and `S80ui` *mention* `helix` and (at the time)
    `SAFE-MODE`, so the checks passed with the logic deleted.
  - `case-ui` went with the helix-only decision.

## Bugs these caught

Not theoretical. Writing them caught real bugs before any hardware was
involved:

- backups were taken *after* the stock `run.sh` had already overwritten the
  files, so a restore would have restored the modified versions
- `rm -rf $MODDIR/bin` with an unset `MODDIR` expands to `rm -rf /bin`
- a crashed UI is a *zombie*, and `kill -0` succeeds on a zombie — the crash
  detector called a dead UI healthy
- the packer emitted both models' filenames from one build, which would have
  handed a Creator 5 the Pro's firmware
- three checks in the brick lint had been quietly dead for months: two were
  guarded on a `payload/boot.sh` that no longer existed, and the file glob
  never matched `firmwareExe` or the `init.d/S*` scripts at all
- a skip counted as a pass for the whole life of the suite, which is how
  `test-abi` sat in it for months checking nothing while printing green