Flutter golden testing

Flutter Golden Testing Skill

This skill outlines the step-by-step process for implementing and updating golden tests for Flutter widgets.

Step 1: Validation & Setup

1. Check Dependencies: Ensure alchemist is present in the dev_dependencies of pubspec.yaml. If it is missing, install it:

   flutter pub add --dev alchemist
   

2. Directory Structure: Create a goldens/ directory adjacent to your target test file to store the generated .png reference files.

Step 2: Test Scaffolding

Create the test file named [widget_name]_test.dart (or [widget_name]_golden_test.dart).

1. Imports: Import the necessary packages (package:flutter_test/flutter_test.dart and package:alchemist/alchemist.dart).
2. Setup Fonts/Assets: Call loadAppFonts() (if applicable) before running the tests to prevent text from rendering as the Ahem font.

Step 3: Implementation

Implement the test using alchemist APIs instead of the standard testWidgets.

1. Use goldenTest: Define your test using the goldenTest function.
2. Mock Externalities:
   • Disable or replace infinite animations (e.g., CircularProgressIndicator).
   • Mock network image requests (e.g., using mocktail_image_network or network_image_mock).
3. Matrix Testing: Use GoldenTestGroup and GoldenTestScenario to lay out all possible widget states (e.g., loading, success, error) and variations (light/dark mode, text scaling) within a single test execution.

Step 4: Generation and Verification

1. Generate Goldens: Run the following command to generate or update the reference images:

   flutter test --update-goldens
   

2. Verify Output: Check that the .png files were correctly generated in the goldens/ directory.
3. Gitignore Failures: Ensure **/failures/ is in the project's .gitignore so test failure artifacts are not accidentally committed.

Step 5: Updating Existing Goldens

If you are modifying an existing widget that already has golden tests, run the update command (flutter test --update-goldens) to regenerate the images. Never modify the .png files manually.