implement-feature

name	implement-feature
description	Implement features from task specifications using Test-Driven Development (TDD) with bmad-commands for file operations and testing. This skill should be used when implementing new functionality from approved task specs.
acceptance	[{"tests_passing":"All tests must pass"},{"coverage_threshold":"Test coverage >= 80%"},{"no_syntax_errors":"Code must have no syntax errors"},{"task_spec_loaded":"Task specification successfully loaded"},{"requirements_met":"All acceptance criteria from task spec addressed"}]
inputs	{"task_id":{"type":"string","required":true,"description":"Task identifier (e.g., task-auth-002-login)","validation":"Must match pattern: task-{component}-{number}-{slug}"},"subtask_id":{"type":"string","required":false,"description":"Optional subtask identifier to implement only a specific subtask (e.g., subtask-1, subtask-2)","validation":"Must match pattern: subtask-{number} if provided"}}
outputs	{"implementation_complete":{"type":"boolean","description":"Whether implementation is complete and meets all criteria"},"test_coverage_percent":{"type":"number","description":"Test coverage percentage achieved"},"files_modified":{"type":"array","description":"List of files created or modified"},"tests_passed":{"type":"boolean","description":"Whether all tests passed"}}
telemetry	{"emit":"skill.implement-feature.completed","track":["task_id","test_coverage_percent","duration_ms","files_modified_count","tests_total","tests_passed","tests_failed"]}

Implement Feature Skill

Purpose

Implement features from task specifications or user stories using Test-Driven Development (TDD). This skill writes tests first, implements code to make tests pass, and validates the implementation meets all acceptance criteria.

Core Principles:

• Test-Driven Development (Red → Green → Refactor)
• Deterministic operations via bmad-commands
• Automated acceptance criteria verification
• Continuous validation

Prerequisites

• Task specification exists at workspace/tasks/{task_id}.md
• bmad-commands skill available at .claude/skills/bmad-commands/
• Development environment configured
• Test framework installed (Jest or Pytest)

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Workflow

Step 0: Load Task Specification

Action: Use bmad-commands to load task spec.

Execute:

python .claude/skills/bmad-commands/scripts/read_file.py \
  --path workspace/tasks/{task_id}.md \
  --output json

Parse Response:

• Verify success == true
• Extract outputs.content for task specification
• Parse sections: Objective, Acceptance Criteria, Context, Tasks

If task spec not found:

• Error: file_not_found in errors array
• Action: Create task spec first using create-task-spec skill
• Halt implementation

If subtask_id is provided:

• Parse the task specification to locate the specific subtask section
• Filter acceptance criteria to only those related to the subtask
• Scope implementation to only the subtask requirements
• Note: All workflow steps below apply only to the selected subtask

See: references/templates.md for required task spec format

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Step 1: Analyze Requirements

Action: Break down acceptance criteria into test cases.

For each acceptance criterion:

1. Identify what needs to be tested (behavior/outcome)
2. Determine test type (unit/integration/e2e)
3. Plan test structure and data
4. Identify edge cases