Testing Setup

Step 1: analyze the current testing setup

To understand the testing setup of an existing project, look for these dependencies in the libs.versions.toml file, or build files:

1. Dependency Injection framework used. Examples: Hilt, Koin, Anvil, vanilla Dagger...
2. Unit (local) testing framework this project uses, Example JUnit4, JUnit5...
3. Mocking framework (if any) used for unit tests, and for Instrumented and UI tests. Examples: Mockito, Mockk...
4. Robolectric. It can be used in 3 ways:
   1. Used in unit tests to have fakes for platform entities
   2. To run behavior UI tests without a device or emulator. For example, used to run Espresso or Compose tests.
   3. To do screenshot testing with Roborazzi
5. Is the app 100% Compose, Views or hybrid?
6. Behavior UI tests:
   1. Compose Tests (androidx.compose.ui:ui-test-*)
   2. Espresso Tests for Views. Might use wrappers like Kaspresso. Dependencies: androidx.test.espresso:espresso-core, androidx.test:runner, androidx.test:rules.
7. Screenshot tests can be:
   1. Instrumented (device-based). For example, using Dropshots.
   2. Based on Robolectric, so they run locally. For example, using Roborazzi.
   3. Based on LayoutLib, so they run locally. For example, Paparazzi, or the Compose Preview Screenshot Testing tool.
8. End to end tests (also known as Release Candidate tests) always run on device and use high-level frameworks such as UIAutomator, Appium, or Robotium.
9. Generate a Markdown report with the analysis

Step 2: Set up Dependency Injection frameworks for testing

If there is no Dependency Injection framework, install one: if it's a multiplatform application, ask the user whether they want to install Koin, or kotlin-inject. If it's not multiplatform, install Hilt.

Install the testing dependencies (for example com.google.dagger:hilt-compiler that should be applied with a kspAndroidTest configuration).

[!IMPORTANT] Important: Always consult the documentation of the applicable framework to learn about testing (for example: Hilt testing guide, Koin Instrumented tests).

For instrumented tests, create and configure (by adding testInstrumentationRunner to the build gradle files) a new test runner and apply the testing rules required by the framework (for example in Hilt, annotate your test classes with @HiltAndroidTest and apply the HiltAndroidRule). Other frameworks use other mechanisms, consult their documentation.

Step 3: Install frameworks

Unless otherwise specified, respect the current stack of testing frameworks.

If there are no testing frameworks, and the user didn't specify any preference, install the following:

• JUnit4 for local and instrumented tests
• Jacoco for test coverage
• For UI tests: if the project has views, Espresso. If it's fully Compose, use the Compose Testing APIs.
• Robolectric to run UI Tests
• Compose Preview Screenshot Testing tool for screenshot tests - check setup documentation and follow it strictly.
• Dropshots for device screenshot tests
• If a mocking framework is necessary, install Mockk (io.mockk:mockk). Do not install it unless it is clearly necessary.

If instrumented screenshot tests are requested, install Dropshots.

If end-to-end testing is requested, install UI Automator.

Step 4: Refactor and create fakes for testing

Refactor for unit tests

In the next sections you'll be asked to create tests. If you have dependencies on Android framework classes, or entities that are not part of the codebase:

• First, use a fake. If it doesn't exist, create an interface for the class and a "Default" implementation with the existing code. Add the Fake version to the test sourceset (test or androidTest).

• If not possible to use a fake (example: no access to the class or interface), mock the dependencies.

Refactor for UI tests

If you need to fake components to make testing easier and faster and more reliable, replace slow and problematic dependencies with fakes. Use runtime fakes using the Dependency Injection framework installed to:

• Simulate different scenarios with the user (wrong credentials, reset password flow...), with a server (no connection, server down, bad JSON from server...) or with a platform component (insufficient permissions, no disk space, no front camera available)
• Improve speed and reliability (replacing a database with an in-memory database, replacing a repository with an in-memory fake to avoid hitting the network)

Step 5: Unit testing

Create a task to add or review unit tests in every file that contains business logic (ViewModels, Repositories, database-related classes such as DAOs, etc.). Don't create unit tests for Activities, Compose layouts, or dependency injection configuration files.

Step 6: UI testing

Espresso or Compose UI tests live in the test sourceset because they will be run with Robolectric. If instrumented (emulator or device) tests are requested, put them in the androidTest sourceset.

Step 7: Test databases

If the database is using SQLite (using Room, SQLDelight, etc.), create instrumented tests using an in-memory database to make sure that they work with the SQLite engine on device.

Step 8: Screenshot tests

Irrespective of the framework used, screenshot tests focus on 2 types of tests:

• Screen-level screenshot tests, where each screen is tested in 9 different sizes, combining compact, medium and expanded widths (400, 610, 900 dp) and heights (400, 500 and 1000 dp).
• Screen-level variations. Add a mobile (400x500) screenshot of:
  • All the alternative themes, if used.
  • Font scale set to 1.5.
• Component-level screenshot tests, where each component is tested in different themes and font scales.

Behavior isn't tested with screenshots, but do test different common scenarios if their UIs change a lot depending on the state. For example, test loading screens by injecting a loading state to the UI or simulating it with a fake.

Step 9: UI Behavior tests

Test the UI logic using behavior tests, which ensures that the UIs react as expected when different states are passed, and when user actions are performed.

Compose UI behavior tests

• Use the ComposeTestRule with a ComponentActivity to access resources such as strings.
• Always try to match with semantic matchers first. If the matcher is too complicated to write (using more than 3 matchers to find a single element), use testTag.
• Always verify state restoration

Views (XML) UI behavior tests

Use Espresso to match views and interact with them.

Step 10: Navigation tests

Create a test suite to verify navigation logic. Include:

• Back handling
• Deeplinks
• Special patterns like "exit through home" with multiple backstacks.

Step 11: Simulate different window sizes and settings

For Compose layouts, use DeviceConfigurationOverride described in "UI testing common patterns" to simulate different window sizes, font scales

Step 12: End-to-end tests

Create a low number (about 5% of all tests) of end-to-end tests that cover big user journeys. Use Compose Test APIs or Espresso for that. If you have to access platform features (notifications, system UI...), use UI Automator.

If you need to take screenshots of the app running in a device, use Dropshots. You need a device for screenshot tests when verifying interaction with the system UI (examples: edge-to-edge rendering, notifications, picture-in-picture)

Step 13: Instrumented Screenshot tests

Install the com.dropbox.dropshots plugin in the module and a Dropshots() JUnit Rule. Create a new instrumented screenshot test for one of the app's features.

Step 14: Install jacoco

Install jacoco for local testing code coverage.

• Add the jacoco plugin to each module that contains tests.

Final touches

• Ask whether to document the findings of the analysis and the changes applied to the testing strategy. If the user agrees:

  • If there is an AGENTS.md file present in the project, update it with any changes you've made to the testing strategy.

  • If there is no AGENTS.md file, create a new file (docs/testing.md) with a description of the testing strategy, including the commands needed to run every type of test, where the screenshot reference files live, etc. Also create a new AGENTS.md file in the root and create a link to docs/testing.md.

Source: android/skills → testing/testing-setup/SKILL.md