docker-testing.md

Docker Testing

Running tests in Docker

Screenshot tests depend on exact browser rendering, which varies across OS and browser versions. Use bin/dtest to run tests inside Docker for consistent, reproducible results matching CI:

bin/dtest                          # Run all tests with all drivers
bin/dtest test/integration/        # Run specific test directory

This builds a Docker image with Chrome and runs the test suite against three Capybara drivers: cuprite, selenium_chrome_headless, and selenium_headless.

Recording baseline screenshots

This page is for contributors to this gem, not for users of it. bin/dtest and RECORD_SCREENSHOTS are this repository's own test harness. RECORD_SCREENSHOTS is read by test/test_helper.rb — it is not a feature of the library and does nothing in your application. To accept a change in your own app, see Accepting an intentional change.

Screenshot baselines are committed to the repo and compared against during tests. When you set up the project for the first time, or after upgrading the browser/driver, you need to re-record them:

RECORD_SCREENSHOTS=1 bin/dtest

This skips screenshot comparisons and saves new baselines instead. Without this step, tests will fail because your local browser renders pixels differently from the previously committed baselines.

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