incremental-implementation

Incremental Implementation

Overview

"Each increment should leave the system in a working, testable state." Build features in small, verifiable steps — each one compiles, passes tests, and can be committed. Never leave the codebase in a broken state between increments.

When to Use

• Implementing any feature from a task breakdown (follows planning-and-task-breakdown)
• Building any change that spans more than one file
• Any time you're tempted to "get it all working, then commit"

Skip when: A true single-file, single-function change.

Core Process

Step 1: Review the Task

1. Read the task's acceptance criteria from tasks/todo.md
2. Identify the vertical slice — what observable behavior does this increment deliver?
3. Gather existing examples — find similar patterns already in the codebase

Step 2: Implement with TDD

1. For each increment, follow this cycle:

┌─────────────────────────────────────────────┐
│  1. Review acceptance criteria              │
│  2. Read existing patterns in codebase      │
│  3. Write failing test (RED)                │
│  4. Write minimal code to pass (GREEN)      │
│  5. Run ./gradlew test                      │
│  6. Run ./gradlew assembleDebug             │
│  7. Commit                                  │
│  8. Repeat for next acceptance criterion    │
└─────────────────────────────────────────────┘

1. Never skip the build check — ./gradlew assembleDebug must succeed after every increment

Step 3: Primary Slicing Strategies

1. Vertical slice (preferred):

   • End-to-end: Entity → DAO → Repository → UseCase → ViewModel → Screen
   • Each slice delivers user-visible functionality
   • Example: "User can view task list" before "User can add task"

2. Contract-first:

   • Define the interface first (Repository interface, API contract)
   • Implement against the contract
   • Useful for parallel development (one dev does UI, another does data layer)

3. Risk-first:

   • Build the most uncertain piece first
   • If the risk materializes, you've spent minimal effort
   • Example: "Can we integrate with the payment SDK?" before building the checkout UI