element-android/docs/screenshot_testing.md

Screenshot testing

• Overview
• Setup
• Recording
• Verifying
• Contributing
• Example

Overview

• Screenshot tests are tests which record the content of a rendered screen and verify subsequent runs to check if the screen renders differently.
• Element uses Paparazzi to render, record and verify android layouts.
• 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 recordScreenshots
• Paparazzi will generate images in ${module}/src/test/snapshots, which will need to be committed to the repository using Git LFS.

Verifying

• ./gradlew verifyScreenshots
• In the case of failure, Paparazzi will generate images in ${module}/out/failure. The images will show the expected and actual screenshots along with a delta of the two images.

Contributing

• When creating a test, the file (and class) name names must include ScreenshotTest, eg ItemScreenshotTest.
• After creating the new test, record and commit the newly rendered screens.
• ./tools/validate_lfs can be ran to ensure everything is working correctly with Git LFS, the CI also runs this check.

Example

class PaparazziExampleScreenshotTest {

    @get:Rule
    val paparazzi = Paparazzi(
            deviceConfig = PIXEL_3,
            theme = "Theme.Vector.Light",
    )

    @Test
    fun `example paparazzi test`() {
        // Inflate the layout
        val view = paparazzi.inflate<ConstraintLayout>(R.layout.item_radio)

        // Bind data to the view
        view.findViewById<TextView>(R.id.actionTitle).text = paparazzi.resources.getString(R.string.room_settings_all_messages)
        view.findViewById<ImageView>(R.id.radioIcon).setImageResource(R.drawable.ic_radio_on)

        // Record the bound view
        paparazzi.snapshot(view)
    }
}