Snapshot testing

lightweight-pdf-testing renders a PDF’s pages to PNG with pdftoppm (poppler-utils) and compares each page against a checked-in reference image, with a small per-pixel tolerance for renderer noise. It works on any PDF, not only ones built with this library.

[dev-dependencies]
lightweight-pdf-testing = "0.3"

let dir = std::path::Path::new("test-fixtures/snapshots");
lightweight_pdf_testing::assert_snapshot(dir, "invoice", &render());

• assert_snapshot(dir, name, pdf_bytes) panics on a mismatch.
• check_snapshot(dir, name, pdf_bytes, dpi, tolerance) returns a Result instead, with your own resolution and tolerance.
• Reference images are low-DPI grayscale PNGs on purpose: a regression trip-wire, not a print-quality proof, and small enough to keep the repository history small.
• On a failed comparison a .diff.png is written next to the reference.

After an intentional visual change, rewrite the references:

UPDATE_SNAPSHOTS=1 cargo test

This repository uses it in crates/lightweight-pdf/tests/snapshots.rs for a handful of representative documents (table and theme, image and watermark, multi-page list and table of contents); see development.