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Golden test fixtures — provenance & regeneration

The three reference FAT12 images under core/src/testFixtures/resources/golden/ are used by Fat12FormatterTest to byte-validate this engine's Fat12Formatter output against mkfs.fat (claim C-C, mkfs.fat golden conformance). They are committed as read-only inputs; they are not regenerated by the build.

Tool version

Generated with dosfstools 4.2 (mkfs.fat / fsck.fat 4.2, 4.2-1.2build1 on Ubuntu 24.04). The CI workflow installs dosfstools on ubuntu-latest (also 4.2) and asserts mkfs.fat --version reports 4.2 so the conformance baseline cannot silently drift to a different upstream. The committed images are not regenerated by default — they are authentic 4.2 output, verified reproducible (below).

Generation commands

Each image is created with mkfs.fat -F 12, a pinned volume serial (-i), and a pinned label (-n). mkfs.fat 4.2 stamps the volume-label directory entry with a creation timestamp; to make the output byte-for-byte reproducible, pin it with SOURCE_DATE_EPOCH (the committed images were stamped 2026-06-08 19:39:04 UTC):

export SOURCE_DATE_EPOCH=1780947544   # 2026-06-08 19:39:04 UTC

mkfs.fat -F 12 -n "TEST1440K" -i a58bab35 -C fat12_1440k_empty.img 1440
mkfs.fat -F 12 -n "TEST720K"  -i a58bc8c6 -C fat12_720k_empty.img 720
mkfs.fat -F 12 -n "TEST360K"  -i a58bded5 -C fat12_360k_empty.img 360
  • -C <file> <N> creates <file> of N × 1024 bytes (1440/720/360 KiB), then writes the filesystem into it.
  • -i <volid> pins the 32-bit volume serial (otherwise random per run).
  • SOURCE_DATE_EPOCH pins the label-entry timestamp. Without it, regenerated images are identical to the committed goldens except for 7 timestamp bytes in the volume-label root-directory entry. With it, regeneration is byte-for-byte identical (cmp reports no difference) under dosfstools 4.2.

Each committed image was confirmed fsck.fat -n-clean (exit 0, no warnings).

Goldens

File Size Geometry
core/src/testFixtures/resources/golden/fat12_1440k_empty.img 1 474 560 B 1.44 MB floppy
core/src/testFixtures/resources/golden/fat12_720k_empty.img 737 280 B 720 KB floppy
core/src/testFixtures/resources/golden/fat12_360k_empty.img 368 640 B 360 KB floppy

Fat12FormatterTest byte-compares the engine's formatter output against these images.

Independent fsck oracle (CI)

Separately from the golden byte-comparison, CI runs an independent dosfstools oracle: ./gradlew :core:fsckEmit writes two engine-produced images (core/build/fsck/fresh.img, core/build/fsck/ops.img) and CI runs fsck.fat -n on both (both must exit 0). This validates the engine's writes against a real third-party FAT checker rather than against mkfs.fat output — a non-circular conformance signal.