Red-Green-Refactor with TestLink

This tutorial walks you through the classic TDD cycle—Red, Green, Refactor—while integrating TestLink at each phase.

What You'll Build

We'll build a StringCalculator class that adds numbers from a string input. This is a classic TDD kata.

Prerequisites

• Completed Getting Started
• TestLink installed in your project

The TDD Cycle with Links

┌─────────────────────────────────────────────────────────────┐
│                                                             │
│    ┌─────────┐      ┌─────────┐      ┌───────────┐         │
│    │  RED    │ ───→ │  GREEN  │ ───→ │ REFACTOR  │         │
│    │         │      │         │      │           │         │
│    │ + test  │      │ + code  │      │ + cleanup │         │
│    │ + link  │      │ + link  │      │ ± links   │         │
│    └─────────┘      └─────────┘      └───────────┘         │
│         ↑                                   │               │
│         └───────────────────────────────────┘               │
│                                                             │
└─────────────────────────────────────────────────────────────┘

Iteration 1: Empty String Returns Zero

Red Phase: Write a Failing Test

Create the test file and write your first test:

<?php
// tests/StringCalculatorTest.php

use App\StringCalculator;

test('returns zero for empty string', function () {
    $calculator = new StringCalculator();

    expect($calculator->add(''))->toBe(0);
})->linksAndCovers(StringCalculator::class.'::add');

Run the test—it fails because StringCalculator doesn't exist:

./vendor/bin/pest
# Error: Class "App\StringCalculator" not found

Green Phase: Make It Pass

Create the minimal production code:

<?php
// src/StringCalculator.php

namespace App;

use TestFlowLabs\TestingAttributes\TestedBy;

class StringCalculator
{
    #[TestedBy('Tests\StringCalculatorTest', 'returns zero for empty string')]
    public function add(string $numbers): int
    {
        return 0; // Minimal implementation
    }
}

Run the test—it passes:

./vendor/bin/pest
# ✓ returns zero for empty string

Validate the links:

./vendor/bin/testlink validate
# ✓ All links are valid!

Refactor Phase

No refactoring needed yet. The code is minimal.

Iteration 2: Single Number Returns Itself

Red Phase

Add a new test:

test('returns the number for single number', function () {
    $calculator = new StringCalculator();

    expect($calculator->add('5'))->toBe(5);
})->linksAndCovers(StringCalculator::class.'::add');

Run tests—the new one fails:

./vendor/bin/pest
# ✓ returns zero for empty string
# ✗ returns the number for single number

Green Phase

Update the production code:

<?php
// src/StringCalculator.php

namespace App;

use TestFlowLabs\TestingAttributes\TestedBy;

class StringCalculator
{
    #[TestedBy('Tests\StringCalculatorTest', 'returns zero for empty string')]
    #[TestedBy('Tests\StringCalculatorTest', 'returns the number for single number')]
    public function add(string $numbers): int
    {
        if ($numbers === '') {
            return 0;
        }

        return (int) $numbers;
    }
}

Run tests—both pass:

./vendor/bin/pest
# ✓ returns zero for empty string
# ✓ returns the number for single number

Refactor Phase

No refactoring needed yet.

Iteration 3: Two Numbers

Red Phase

test('returns sum of two numbers', function () {
    $calculator = new StringCalculator();

    expect($calculator->add('1,2'))->toBe(3);
})->linksAndCovers(StringCalculator::class.'::add');

Green Phase

<?php
// src/StringCalculator.php

namespace App;

use TestFlowLabs\TestingAttributes\TestedBy;

class StringCalculator
{
    #[TestedBy('Tests\StringCalculatorTest', 'returns zero for empty string')]
    #[TestedBy('Tests\StringCalculatorTest', 'returns the number for single number')]
    #[TestedBy('Tests\StringCalculatorTest', 'returns sum of two numbers')]
    public function add(string $numbers): int
    {
        if ($numbers === '') {
            return 0;
        }

        $parts = explode(',', $numbers);

        return array_sum(array_map('intval', $parts));
    }
}

Refactor Phase

The code now handles the general case. Previous implementations were stepping stones.

Iteration 4: Multiple Numbers

Red Phase

test('returns sum of multiple numbers', function () {
    $calculator = new StringCalculator();

    expect($calculator->add('1,2,3,4,5'))->toBe(15);
})->linksAndCovers(StringCalculator::class.'::add');

Green Phase

The test passes immediately! Our implementation already handles this case.

./vendor/bin/pest
# ✓ returns zero for empty string
# ✓ returns the number for single number
# ✓ returns sum of two numbers
# ✓ returns sum of multiple numbers

Add the #[TestedBy] attribute anyway:

#[TestedBy('Tests\StringCalculatorTest', 'returns zero for empty string')]
#[TestedBy('Tests\StringCalculatorTest', 'returns the number for single number')]
#[TestedBy('Tests\StringCalculatorTest', 'returns sum of two numbers')]
#[TestedBy('Tests\StringCalculatorTest', 'returns sum of multiple numbers')]
public function add(string $numbers): int

Final Validation

Run a complete validation:

./vendor/bin/testlink validate

Validation Report
─────────────────

Link Summary
  PHPUnit attribute links: 4
  Pest method chain links: 0
  Total links: 4

TestedBy Summary
  TestedBy attributes found: 4
  Synchronized: 4

✓ All links are valid!

View the Report

./vendor/bin/testlink report

Coverage Links Report
─────────────────────

App\StringCalculator

  add()
    → Tests\StringCalculatorTest::returns zero for empty string
    → Tests\StringCalculatorTest::returns the number for single number
    → Tests\StringCalculatorTest::returns sum of two numbers
    → Tests\StringCalculatorTest::returns sum of multiple numbers

Summary
  Methods with tests: 1
  Total test links: 4

Key Takeaways

1. Add test-side links in Red phase - When writing the failing test
2. Add production-side links in Green phase - When making the test pass
3. Update links in Refactor phase - If you rename or restructure
4. Validate frequently - Catch broken links early

What's Next?

• Placeholders - Use placeholders for faster iteration
• Complete Example - A more comprehensive TDD walkthrough