PHP Testing Patterns (stack-agnostic)

Patterns for PHPUnit and Pest that apply to any PHP codebase. Detect which runner the project uses before writing tests: pestphp/pest in require-dev → Pest; otherwise PHPUnit. Both run on top of PHPUnit assertions.

Detection and running

grep -q pestphp/pest composer.json && echo pest || echo phpunit
vendor/bin/phpunit            # PHPUnit
vendor/bin/pest               # Pest
vendor/bin/phpunit --coverage-text   # coverage (needs Xdebug or PCOV)

Prefer a composer test script if one exists.

Test structure — Arrange / Act / Assert

PHPUnit (class-based):

<?php

declare(strict_types=1);

namespace App\Tests\Unit;

use App\Domain\Money;
use App\Domain\Currency;
use PHPUnit\Framework\TestCase;

final class MoneyTest extends TestCase
{
    public function test_it_adds_two_amounts_of_the_same_currency(): void
    {
        // Arrange
        $a = new Money(100, Currency::USD);
        $b = new Money(250, Currency::USD);

        // Act
        $sum = $a->add($b);

        // Assert
        self::assertSame(350, $sum->amount);
    }

    public function test_it_rejects_a_currency_mismatch(): void
    {
        $this->expectException(\InvalidArgumentException::class);

        (new Money(100, Currency::USD))->add(new Money(100, Currency::EUR));
    }
}

Pest (function-based, same engine):

<?php

declare(strict_types=1);

use App\Domain\Money;
use App\Domain\Currency;

it('adds two amounts of the same currency', function () {
    $sum = (new Money(100, Currency::USD))->add(new Money(250, Currency::USD));

    expect($sum->amount)->toBe(350);
});

it('rejects a currency mismatch', function () {
    expect(fn () => (new Money(100, Currency::USD))->add(new Money(100, Currency::EUR)))
        ->toThrow(InvalidArgumentException::class);
});

Naming and organisation

• Tests live in tests/, namespace App\Tests\... (mapped via autoload-dev).
• Mirror the source tree: src/Domain/Money.php → tests/Unit/Domain/MoneyTest.php.
• Split tests/Unit (pure, no I/O) from tests/Integration / tests/Feature (DB, HTTP, filesystem).
• PHPUnit method names: test_it_<behaviour>() or #[Test] attribute. Pest: it('<behaviour>'). Describe behaviour, not implementation.

Data providers / datasets

Drive many cases through one body instead of duplicating tests.

// PHPUnit
public static function discountCases(): array
{
    return [
        'no discount below 100' => [50, 0.0],
        '5% at 100'             => [100, 0.05],
        '15% at 1000'           => [1000, 0.15],
    ];
}

#[DataProvider('discountCases')]
public function test_discount_tiers(int $total, float $expected): void
{
    self::assertSame($expected, discountFor($total));
}

// Pest
it('applies discount tiers', function (int $total, float $expected) {
    expect(discountFor($total))->toBe($expected);
})->with([
    [50, 0.0],
    [100, 0.05],
    [1000, 0.15],
]);

Test doubles — mock collaborators, not the SUT

public function test_it_sends_a_receipt_after_charging(): void
{
    $gateway = $this->createMock(PaymentGateway::class);
    $gateway->expects(self::once())
        ->method('charge')
        ->with(self::equalTo(500))
        ->willReturn(new Receipt('rcpt_1'));

    $mailer = $this->createMock(Mailer::class);
    $mailer->expects(self::once())->method('send');

    $service = new CheckoutService($gateway, $mailer);
    $service->checkout($order);
}

Discipline:

• Stub queries (return canned data); mock commands (assert they were called).
• Mock the collaborators of the unit under test — never mock the class you are testing.
• Don't over-specify: assert the interactions that matter, not every call.
• Prefer real value objects and in-memory fakes over mocks for simple data.

Fixtures — setUp / tearDown

protected function setUp(): void
{
    parent::setUp();
    $this->repository = new InMemoryUserRepository();
}

• Build fresh state per test; do not share mutable state across tests (order-dependence is a bug).
• Use setUp() for common arrange steps; keep heavy fixtures out of unit tests.
• For DB-backed tests, the framework plugin's QA phase supplies isolation (transactions/rollback) — apply that there.

Coverage target

• Aim for ≥80% line coverage on changed code; 100% on domain/business logic.
• Coverage is a floor, not a goal — a covered line is not necessarily an asserted behaviour.
• Run vendor/bin/phpunit --coverage-text (requires PCOV or Xdebug). Report the number; do not chase the last few percent on glue code.