public function testUserCreationSetsDefaults(): void
{
    // Arrange
    $data = ['name' => 'Alice', 'email' => 'alice@example.com'];

    // Act
    $user = User::fromArray($data);

    // Assert
    $this->assertSame('Alice', $user->getName());
    $this->assertTrue($user->isActive());
    $this->assertSame([], $user->getRoles());
}

final class PaymentServiceTest extends TestCase
{
    private PaymentService $service;
    private Gateway&Stub $gateway;

    protected function setUp(): void
    {
        $this->gateway = $this->createStub(Gateway::class);
        $this->service = new PaymentService($this->gateway);
    }
}

use PHPUnit\Framework\Attributes\DataProvider;

#[DataProvider('additionCases')]
public function testAdd(int $a, int $b, int $expected): void
{
    $this->assertSame($expected, $a + $b);
}

public static function additionCases(): array
{
    return [
        'zeros'        => [0, 0, 0],
        'positive sum' => [1, 2, 3],
        'negative'     => [-1, 1, 0],
    ];
}

use PHPUnit\Framework\Attributes\TestWith;

#[TestWith([0, 0, 0])]
#[TestWith([1, 2, 3])]
#[TestWith([-1, 1, 0])]
public function testAdd(int $a, int $b, int $expected): void
{
    $this->assertSame($expected, $a + $b);
}

public static function boundaryCases(): Generator
{
    yield 'min int' => [PHP_INT_MIN, 0, PHP_INT_MIN];
    yield 'max int' => [PHP_INT_MAX, 0, PHP_INT_MAX];
}

$this->assertSame($expected, $actual);        // Strict === (preferred)
$this->assertEquals($expected, $actual);       // Loose == (use sparingly)
$this->assertTrue($condition);
$this->assertFalse($condition);
$this->assertNull($value);
$this->assertInstanceOf(Expected::class, $obj);
$this->assertCount(3, $collection);
$this->assertEmpty($collection);
$this->assertArrayHasKey('key', $array);
$this->assertContains($needle, $haystack);     // Strict comparison

$this->assertStringStartsWith('Error:', $message);
$this->assertStringEndsWith('.php', $filename);
$this->assertStringContainsString('needle', $haystack);
$this->assertMatchesRegularExpression('/^\d{4}-\d{2}$/', $date);

$this->assertEqualsWithDelta(3.14, $result, 0.01);

public function testThrowsOnInvalidInput(): void
{
    $this->expectException(InvalidArgumentException::class);
    $this->expectExceptionMessage('must be positive');

    $calculator->divide(1, 0);
}

public function testTriggersDeprecation(): void
{
    $this->expectUserDeprecationMessage('use newMethod() instead');

    $service->oldMethod();
}

$repo = $this->createStub(UserRepository::class);
$repo->method('find')->willReturn(new User(name: 'Alice'));

$service = new UserService($repo);
$result = $service->getUser(1);

$this->assertSame('Alice', $result->name);

$repo = $this->createConfiguredStub(UserRepository::class, [
    'find'   => new User(name: 'Alice'),
    'exists' => true,
]);

$logger = $this->createMock(Logger::class);
$logger->expects($this->once())
    ->method('error')
    ->with($this->stringContains('payment failed'));

$service = new PaymentService($logger);
$service->process($invalidPayment);

$stub->method('fetch')->willReturn('value');              // Fixed value
$stub->method('fetch')->willReturn('a', 'b', 'c');       // Consecutive values
$stub->method('fetch')->willReturnArgument(0);            // Return first arg
$stub->method('fetch')->willReturnSelf();                 // Fluent interface
$stub->method('fetch')->willReturnCallback(fn ($id) => "item-{$id}");
$stub->method('fetch')->willThrowException(new RuntimeException('fail'));
$stub->method('fetch')->willReturnMap([
    ['key1', 'value1'],
    ['key2', 'value2'],
]);

tests/
├── Unit/                     # Fast, isolated, no I/O
│   ├── Service/
│   │   └── PaymentServiceTest.php
│   └── Model/
│       └── UserTest.php
├── Integration/              # Real dependencies, slower
│   └── Repository/
│       └── UserRepositoryTest.php
└── bootstrap.php             # Autoloader for tests

<testsuites>
    <testsuite name="unit">
        <directory>tests/Unit</directory>
    </testsuite>
    <testsuite name="integration">
        <directory>tests/Integration</directory>
    </testsuite>
</testsuites>

<?xml version="1.0" encoding="UTF-8"?>
<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/11.5/phpunit.xsd"
         bootstrap="vendor/autoload.php"
         colors="true"
         cacheDirectory=".phpunit.cache"
         executionOrder="depends,random"
         beStrictAboutTestsThatDoNotTestAnything="true"
         beStrictAboutOutputDuringTests="true"
         failOnWarning="true"
         failOnRisky="true"
         failOnDeprecation="true"
         failOnNotice="true">
    <testsuites>
        <testsuite name="unit">
            <directory>tests/Unit</directory>
        </testsuite>
        <testsuite name="integration">
            <directory>tests/Integration</directory>
        </testsuite>
    </testsuites>
    <source restrictDeprecations="true"
            restrictNotices="true"
            restrictWarnings="true">
        <include>
            <directory suffix=".php">src</directory>
        </include>
    </source>
</phpunit>

phpunit --coverage-html build/coverage --coverage-clover build/clover.xml

Bad:  "According to PHPUnit best practices, you should use createStub
       instead of createMock when you don't need expectations..."
Good: "createMock → createStub (no expects() call, stub is sufficient)"