Lookalike

Golden image comparison for Ruby graphics.

Features · Installation · Quick Start

Lookalike turns rendered images into visual regression tests. It compares Tessel images, file paths, and framebuffer-like objects, then writes actionable diffs for failed snapshots.

• Channel and YIQ perceptual comparison modes.
• Per-pixel deltas, allowed-pixel limits, bounding boxes, and diff images.
• Optional antialiasing detection for cleaner UI and text snapshots.
• RSpec, Minitest, and Test::Unit assertion helpers.
• Snapshot approval flow for local development and CI.
• HTML reports with an expected/actual overlay slider.

Add Lookalike to your Gemfile:

gem "lookalike"

Then run:

bundle install

Or install the released gem:

gem install lookalike

• Ruby 3.1 or newer.
• Tessel is installed automatically as a runtime dependency.

require "lookalike"

actual = Tessel.read("actual.png")
result = Lookalike.compare("expected.png", actual, mode: :channel, max_delta: 1)
abort result.inspect unless result.match?

For snapshot assertions, include Lookalike::Assertions in the test context:

include Lookalike::Assertions

assert_snapshot(render_scene, "home")

Missing snapshots are pending locally. Approve them with:

LOOKALIKE_UPDATE=1 bundle exec rake
lookalike approve NAME
lookalike approve --all
lookalike report tmp/lookalike

Set CI to make missing snapshots fail.

bundle install
bundle exec rake verify

Bug reports and pull requests are welcome at rbgfx/lookalike.

MIT