EXACT Coding - Exercises

Exercise setup for the EXACT Coding workshop: EXample-guided, AI-Collaborative & Test-driven Development.

Workshop

Test-Driven, AI-Assisted Development for Maintainable Code.

This hands-on workshop introduces EXACT Coding -- a pragmatic workflow for AI-assisted development focusing on readability, refactorability, and maintainability. Participants work in pairs and groups of three (driver + two navigators) through short modules with extensive exercises.

Topics

• Test-Driven Development (TDD)
• Example Mapping
• Mob/Ensemble Programming
• AI Tools (Claude Code and Cursor)
• EXACT Coding Workflow

Trainers

Ferdi Ade & Marco Emrich

Setup

There are two ways to set up the project: using the Dev Container (recommended) or a local installation.

Option A: Dev Container (recommended)

The repo includes a Dev Container configuration with Node.js, Claude Code, and a restrictive firewall pre-installed.

Prerequisites

• Docker
• VS Code with the Dev Containers extension
• Claude Code API key or Portkey configuration (see below)

API Key Configuration

Option 1: Direct API key -- set the environment variable on your host before opening the container:

export ANTHROPIC_API_KEY="sk-ant-..."

Option 2: Portkey proxy -- configure in ~/.claude/settings.json on your host:

{
  "env": {
    "ANTHROPIC_BASE_URL": "https://api.portkey.ai",
    "ANTHROPIC_AUTH_TOKEN": "dummy",
    "ANTHROPIC_CUSTOM_HEADERS": "x-portkey-api-key: <your-key>"
  }
}

The container automatically mounts ~/.claude/ from your host, so your settings are available inside the container.

Starting the Dev Container

1. Open the project folder in VS Code (File -> Open Folder, not as workspace)
2. VS Code will prompt: "Reopen in Container" -- click it
3. Or manually: Ctrl+Shift+P -> "Dev Containers: Reopen in Container"
4. Wait for the container to build (first time takes a few minutes)

After startup, run npm install in the terminal, then verify with the checks below.

Option B: Local Installation

Prerequisites

• Node.js (v20 or higher)
• npm
• Claude Code (npm install -g @anthropic-ai/claude-code)

Installation

npm install

Running Tests

npm test

Watch Mode

npm run test:watch

Verify Your Setup

Run the following checks to make sure everything is working (both local and Dev Container).

1. Node.js installed?

node --version
# Expected: v20 or higher (e.g. v24.9.0)

2. Claude Code installed and API key configured?

claude -p "respond with: setup ok"
# Expected: "setup ok" (or similar short response)

If this hangs or returns an authentication error, your API key is not configured correctly. See the Claude Code docs for setup instructions.

3. Dependencies installed and tests passing?

npm install
npm test

Expected test output:

 ✓ src/example.spec.ts (1 test)

 Test Files  1 passed (1)
      Tests  1 passed (1)

If all checks pass, you're ready for the workshop!

Claude Code Configuration

This repo ships with a preconfigured .claude/ directory that enforces the EXACT Coding workflow when using Claude Code. The configuration consists of Rules, Agents, and Commands.

Rules (.claude/rules/)

Rules are loaded automatically into Claude's context at startup. They define the guardrails for the entire session.

File	Purpose
tdd.md	Core TDD workflow -- mandates the use of specialized agents for every TDD phase
human-in-the-loop.md	Checkpoint rules -- Claude must stop after every phase (Red, Green, Refactor) and wait for explicit approval
tdd_with_ts_and_vitest.md	TypeScript & Vitest conventions (test file naming, imports, test execution)

Agents (.claude/agents/)

Agents are specialized sub-agents that run in an isolated context. Each agent focuses on exactly one TDD phase, preventing context pollution and enforcing discipline.

Agent	Phase	Description
test-list	Test List	Creates it.todo() entries for base functionality, ordered simple to complex
red	Red	Activates ONE test, makes a prediction (Guessing Game), verifies it fails for the right reason
green	Green	Implements the minimal code to make the failing test pass (hardcoded returns are fine!)
refactor	Refactor	Applies the Four Rules of Simple Design and calculates APP mass before/after
code-improvement-scanner	Review	Analyzes code for readability, performance, and best practice improvements

Commands (.claude/commands/)

Commands are slash commands that can be invoked manually during a Claude Code session (e.g. /red, /green, /refactor). They provide the same functionality as agents but run in the main context instead of an isolated one.

Command	Usage
/test-list	Create a test list with it.todo() entries
/red	Enter Red phase -- activate a test and predict the failure
/green	Enter Green phase -- write minimal implementation
/refactor	Refactor using Simple Design Rules and APP
/code-review	Multi-stage code review (Review -> Evaluation -> Conclusion)

Agents vs. Commands

	Agents	Commands
Context	Isolated (fresh context per phase)	Shared (main conversation context)
Invocation	Automatic (via rules)	Manual (/command-name)
Best for	Strict TDD discipline	Quick, interactive use

TDD Workflow

The typical EXACT Coding workflow with Claude Code:

1. Start -- Claude automatically uses the test-list agent to create it.todo() entries
2. Red -- The red agent activates one test, predicts the failure, verifies it fails
3. Green -- The green agent writes minimal code to make the test pass
4. Refactor -- The refactor agent improves the code (naming, duplication, APP mass)
5. Repeat -- Back to step 2 for the next test

After every phase, Claude stops and asks for approval before continuing (Human-in-the-Loop).