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Introduction to snapshot (aka golden) testing (in R)

Build and Deploy Presentation

In this presentation, I introduce what is snapshot testing, why is it necessary, and its implementation in R in {testthat} package and its extensions.

Logos Combined

In particular, the presentation provides a detailed account of how these tests are valuable in testing:

  • text outputs
  • graphical outputs
  • Shiny apps
  • entire files

Slides can be seen here: https://www.indrapatil.com/intro-to-snapshot-testing/

Development

This project uses R 4.6.1 or later (declared in DESCRIPTION), Quarto for rendering slides, and just as a command runner.

Prerequisites

# Install just (macOS)
brew install just

Setup

just install

Just Commands

just help     # Show all available commands
just install  # Install R dependencies and the a11y extension
just sync     # Alias for install
just update   # Update R dependencies
just render   # Render slides to HTML
just preview  # Start a live preview with auto-reload
just open     # Alias for preview (live-reload dev server over localhost)
just clean    # Remove generated files and caches
just check    # Check the Quarto and R version setup
just axe      # Preview with an Accessibility Report slide
just          # Install dependencies and start live-reload preview

just axe enables the opt-in a11y profile. It accepts preview options, for example just axe --no-browser --port 8834. Inspect slide and scroll views, including all fragments and tab panels. Run just render for the production deck, which excludes the audit payload and report.

Accessibility

just install and the shared CI workflow install the latest quarto-revealjs-a11y directly from upstream with quarto add mcanouil/quarto-revealjs-a11y --no-prompt. The extension handles browser zoom, slide isolation, focus indicators, link underlines, reduced motion, and screen-reader announcements.

The accessibility.html helper still handles scrollable code, slide-menu focus, and vertical-slide semantics. It is shared verbatim across the whole presentation fleet — by convention, kept in sync by hand rather than by any automated check — so it carries every branch any deck in the fleet needs, not just the ones this deck exercises. Its tab-ordering and arrow-key block is inert in decks that have no tabsets; this deck does have a panel-tabset, so that block is live here. Do not trim unused branches from the file: change it here and copy the same change to the other decks, never patch a single deck in isolation. The extension's slide-menu patch and accessibility settings panel are disabled as in the reference deck: version 0.2.3 introduces ARIA and contrast failures in those components.

Use just axe to inspect slides, fragments, and menu panels in presentation and scroll views. Normal builds omit the axe checker.

Feedback

Feedback and suggestions are welcome in the issue tracker.