The smoke test used to check a per-example `nonBlack` floor — "at
least one sprite rendered," plus a per-example minimum for the
multi-sprite examples. That catches gross regressions (a compiler
bug that makes everything go black) but silently lets through
anything that changes a handful of pixels without dropping below
the sprite floor. The whole point of this harness is to catch
compiler miscompiles before they land; a softer check means bugs
can still sneak in.
This swap makes every run diff the raw canvas framebuffer against
a committed PNG golden. One mismatched byte at pixel (120, 119)
is enough to fail CI — there's nowhere for a regression to hide.
Workflow:
# normal — fails on any pixel change
node tests/emulator/run_examples.mjs
# when the diff is intentional, rewrite the goldens
UPDATE_GOLDENS=1 node tests/emulator/run_examples.mjs
# or: node tests/emulator/run_examples.mjs --update-goldens
git diff tests/emulator/goldens/ # review the change
git add tests/emulator/goldens/
git commit # explain WHY in the message
When a run fails without `UPDATE_GOLDENS`, the runner writes:
tests/emulator/actual/<name>.png the run's raw output
tests/emulator/actual/<name>.diff.png red-highlighted pixel diff
so reviewers can eyeball what changed without rerunning locally.
`actual/` is gitignored and re-created on every run. The CI job
now uploads `actual/`, `goldens/`, and `report.json` together as
a single `emulator-diff` artifact on failure — side by side means
the "what changed" story is obvious without cloning.
Implementation:
- `tests/emulator/screenshots/` is renamed to `tests/emulator/goldens/`.
All 18 existing PNGs are preserved as the initial goldens (git
detected them as pure renames).
- `harness.html` gets a new `window.nesHarness.rawPixelsBase64()`
that returns the 245760-byte (256 × 240 × 4 bytes) RGBA canvas
buffer as base64. The runner compares raw pixels, not PNG
bytes, so encoder quirks (zlib level, filter heuristics) can't
cause false positives across Chrome versions or platforms.
- The runner uses `pngjs` (pure-JS, no native deps) to decode
goldens and to write diff PNGs. `PNG.sync.write` is
byte-deterministic for identical pixels, so `git diff` on a
committed golden only ever shows up when the actual rendered
pixels changed — not because two machines produced slightly
different compression.
- The committed goldens were re-encoded with pngjs in this commit
so the baseline is consistent from day one. File sizes are a
touch larger than Chrome's output (~1KB vs ~800B on average),
but that's negligible and it eliminates one entire class of
flaky-looking diffs in the future.
Determinism verification: I ran each of the 18 ROMs twice
through fresh `NES` instances in fresh puppeteer pages, hashed
the 245760-byte framebuffers at frame 180 with SHA-256, and
confirmed `run1 == run2` for every single one. Exact-pixel diffs
are safe for this ROM set.
Negative path verification: I corrupted one golden (flipped one
pixel to pure red via pngjs) and reran the runner. It printed
DIFF hello_sprite 1/61440 pixels differ; first at (120,120)
expected [255,0,0] got [0,0,0]
actual: tests/emulator/actual/hello_sprite.png
diff: tests/emulator/actual/hello_sprite.diff.png
and exited 1 as expected. The diff PNG shows a dim-grayscale
silhouette of the expected frame with a bright-red dot on the
one mismatched pixel — enough visual context to locate the
regression at a glance.
All 18 examples match their goldens in strict mode. `cargo fmt
--check`, `cargo clippy --release --all-targets -- -D warnings`,
and `cargo test --release` (313 unit + 37 integration) are all
still green.
https://claude.ai/code/session_014Z5y3Q9krLcAxYpZQJhZ5V
Running the compiled example ROMs through a headless puppeteer +
local jsnes harness exposed four latent bugs that the
header-structure-only integration tests couldn't catch:
- src/asm/mod.rs: the first pass treated ANY instruction with
`AddressingMode::Label` as a label definition, silently dropping
every `JMP`/`JSR` to a label. Now only `NOP + Label` is a label
def; other opcodes emit the opcode byte plus a 2-byte absolute
fixup resolved in pass two. Without this, every example crashed
with "invalid opcode at $1xxx" once the CPU fell through into
the math runtime and hit an unbalanced `RTS`.
- src/ir/lowering.rs (lower_handler): handler-local `VarDecl`s
(e.g. `var i: u8 = 0` inside a `while`) were pushed onto
`current_locals` but the handler built its own throwaway
`locals` list, so those var ids never got RAM addresses and
every `LoadVar`/`StoreVar` for them silently emitted nothing.
Seed `current_locals` with the state's declared locals and
reuse it so `lower_statement`'s appends flow through to the
`IrFunction`. Fixes the black screen in `arrays_and_functions`.
- src/ir/lowering.rs (global init): struct-literal initializers
on globals (`var player: Player = Player { x: 120, ... }`) fell
through to `eval_const`, which returned `None` for a
non-literal, so no init code was emitted. Now the per-field
synthetic globals each get their own `init_value`. Fixes the
black screen in `structs_enums_for`.
- src/codegen/mod.rs: the legacy AST codegen was emitting
`JSR __fn_poke` / treating `peek` as `LDA #0` for the hardware
intrinsics. It only "worked" before because the broken
assembler swallowed the bogus JSR. Handle `poke`/`peek` as
direct STA/LDA to a compile-time-constant absolute address,
matching the IR codegen's intrinsic path.
The harness lives in `tests/emulator/`: a tiny HTML page that
wraps the `jsnes` npm package, driven by a puppeteer script that
loads each ROM, runs ~180 frames, snapshots the canvas, and
records a smoke-test verdict (booted without a CPU crash, non-zero
pixels rendered, frames differ over time). `npm install && node
run_examples.mjs` from `tests/emulator/` runs the full sweep.
9/9 example ROMs now load, render, and animate where expected.
All 324 unit + 35 integration tests still pass.
https://claude.ai/code/session_014Z5y3Q9krLcAxYpZQJhZ5V
