tdd-dart-coder

name	tdd-dart-coder
description	Guides the Coder subagent in updating Dart library code to pass failing tests.

TDD Dart Coder Skill

Objective

To write robust, idiomatic Dart implementation code that makes failing tests pass.

Core Rules & Constraints

1. Directory Boundary: You are ONLY allowed to write or modify files inside the <dart_package_dir>/lib/ directory (e.g. <dart_package_dir>/lib/src/<module_name>.dart) and <dart_package_dir>/example/ (during Phase 5). You must NEVER edit files in test/ or specs/.
2. Minimal Edit Rule: Focus on making the failing tests pass. Avoid adding unrequested features or changing public signatures not specified in the Architect's specification.
3. Code Generation Rule: If the target package uses code generation (e.g., package:json_serializable or freezed), run dart run build_runner build --delete-conflicting-outputs inside <dart_package_dir>/ after updating files to generate the required .g.dart or .freezed.dart output.
4. Iterable Builder Collections Rule: When implementing fluent APIs that output wrapper collections (such as transitions list builders, DSL parameter maps, or child node groups), make the custom class implement Iterable<T> or provide an explicit collection getter (e.g., .items, .transitions, or .list). This allows client configurations to use Dart's spread operator (...) cleanly without compiler errors.

Workflow

1. Read the specification file in <dart_package_dir>/specs/<module_name>_spec.md and the failing tests in <dart_package_dir>/test/<module_name>_test.dart.
2. Create or update files in lib/ (typically inside <dart_package_dir>/lib/src/ and exporting through the main <dart_package_dir>/lib/<package_name>.dart library entry point).
3. Ensure the implementation resolves all test assertions.
4. Run dart format on any files you edit to maintain code quality.
5. End your turn by notifying the parent Coordinator of the completed implementation.