letro-android/docs/screenshot_testing.md

Screenshot testing

• Overview
• Setup
• Recording
• Verifying
• Contributing

Overview

• Screenshot tests are tests which record the content of a rendered screen and verify subsequent runs to check if the screen renders differently.
• ElementX uses Paparazzi to render, record and verify Composable. All Composable Preview will be use to make screenshot test, thanks to the usage of Showkase.
• The screenshot verification occurs on every pull request as part of the tests.yml workflow.

Setup

• Install Git LFS through your package manager of choice (brew install git-lfs | yay -S git-lfs).
• Install the Git LFS hooks into the project.

# with element-android as the current working directory
git lfs install --local

If installed correctly, git push and git pull will now include LFS content.

Recording

./gradlew recordPaparazziDebug

The task will delete the content of the folder /snapshots before recording (see the task removeOldSnapshots defined in the project).

If this is not the case, you can run

rm -rf ./tests/uitests/src/test/snapshots

Paparazzi will generate images in :tests:uitests/src/test/snapshots, which will need to be committed to the repository using Git LFS.

Verifying

./gradlew verifyPaparazziDebug

In the case of failure, Paparazzi will generate images in :tests:uitests/out/failure. The images will show the expected and actual screenshots along with a delta of the two images.

Contributing

• Creating Previewable Composable will automatically creates new screenshot tests.
• After creating the new test, record and commit the newly rendered screens.
• ./tools/git/validate_lfs.sh can be run to ensure everything is working correctly with Git LFS, the CI also runs this check.