테스트 주도 개발 워크플로

테스트 주도 개발은 설계 도구입니다

레드, 그린, 리팩터링

레드: 실패하는 테스트를 먼저 작성하기

<?php
use PHPUnit\Framework\TestCase;

final class PriceCalculatorTest extends TestCase
{
    public function test_applies_a_percentage_discount(): void
    {
        $calc = new PriceCalculator();
        // 100 with 10% off -> 90.0
        self::assertSame(90.0, $calc->withDiscount(100.0, 10));
    }
}

그린: 통과에 필요한 최소 코드

<?php
final class PriceCalculator
{
    public function withDiscount(float $amount, float $percent): float
    {
        return $amount - ($amount * $percent / 100);
    }
}

$calc = new PriceCalculator();
var_dump($calc->withDiscount(100.0, 10)); // float(90)

일반성을 이끌어 내는 삼각 측량

<?php
use PHPUnit\Framework\TestCase;

final class PriceCalculatorTest extends TestCase
{
    public function test_zero_percent_is_unchanged(): void
    {
        self::assertSame(50.0, (new PriceCalculator())->withDiscount(50.0, 0));
    }

    public function test_full_discount_is_free(): void
    {
        self::assertSame(0.0, (new PriceCalculator())->withDiscount(50.0, 100));
    }
}

경계 사례를 사양으로 이끌어 내기

<?php
use PHPUnit\Framework\TestCase;

final class PriceCalculatorValidationTest extends TestCase
{
    public function test_rejects_negative_discount(): void
    {
        $this->expectException(\InvalidArgumentException::class);
        (new PriceCalculator())->withDiscount(100.0, -5);
    }
}

다시 그린으로, 그런 다음 리팩터링

<?php
final class PriceCalculator
{
    public function withDiscount(float $amount, float $percent): float
    {
        if ($percent < 0 || $percent > 100) {
            throw new \InvalidArgumentException('percent must be 0..100');
        }
        return round($amount - ($amount * $percent / 100), 2);
    }
}

var_dump((new PriceCalculator())->withDiscount(19.99, 15)); // float(16.99)

데이터 제공자로 예를 압축하기

<?php
use PHPUnit\Framework\TestCase;
use PHPUnit\Framework\Attributes\DataProvider;

final class DiscountTableTest extends TestCase
{
    #[DataProvider('cases')]
    public function test_discounts(float $amount, float $pct, float $expected): void
    {
        self::assertSame($expected, (new PriceCalculator())->withDiscount($amount, $pct));
    }

    public static function cases(): array
    {
        return [
            'no discount'   => [100.0, 0, 100.0],
            'ten percent'   => [100.0, 10, 90.0],
            'free'          => [100.0, 100, 0.0],
        ];
    }
}

주기를 빠르게 유지하기

vendor/bin/phpunit --testdox --filter PriceCalculator

테스트도 리팩터링하기

<?php
use PHPUnit\Framework\TestCase;

final class PriceCalculatorTest extends TestCase
{
    private PriceCalculator $calc;

    protected function setUp(): void
    {
        $this->calc = new PriceCalculator(); // shared setup, no duplication
    }

    public function test_ten_percent(): void
    {
        self::assertSame(90.0, $this->calc->withDiscount(100.0, 10));
    }
}

테스트 주도 개발이 의존성을 형성합니다

<?php
interface RoundingPolicy { public function round(float $v): float; }

final class PriceCalculator
{
    public function __construct(private RoundingPolicy $rounding) {}

    public function withDiscount(float $amount, float $percent): float
    {
        return $this->rounding->round($amount - ($amount * $percent / 100));
    }
}
// Tests inject a deterministic RoundingPolicy; no hidden global behavior.

빠른 확인

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