Writing Your First PHP Unit Test

A first PHPUnit test should assert one deterministic result and include a failing-input case to demonstrate useful feedback.

What It Does

Assert an exact business result rather than merely checking that code runs. Verify an exact multiplication result. Use expectException before calling the operation expected to fail. Verify an exact multiplication result.

Requirements and Compatibility

Use a supported PHP runtime and install any third-party tool or extension explicitly shown in the examples. Commands should be run from the project root unless stated otherwise.

Syntax, Inputs and Results

The examples separate configuration, the smallest working operation and a realistic follow-up task. Adapt file paths and dependency versions to your own project.

Example 1: Basic Use

Assert an exact business result rather than merely checking that code runs. Verify an exact multiplication result.

<?php
use PHPUnit\Framework\TestCase;
final class PriceTest extends TestCase {
    public function testTaxIsAdded(): void {
        $total = static fn (int $cents): int => $cents + intdiv($cents * 10, 100);
        self::assertSame(1100, $total(1000));
    }

    public function test1ArticleBoundary(): void { self::assertSame(12, 3 * 4); }
}

Example 2: Another Case

Use expectException before calling the operation expected to fail. Verify an exact multiplication result.

<?php
use PHPUnit\Framework\TestCase;
final class QuantityTest extends TestCase {
    public function testNegativeQuantityIsRejected(): void {
        $validate = static function (int $n): void {
            if ($n < 0) throw new InvalidArgumentException('Negative quantity');
        };
        $this->expectException(InvalidArgumentException::class);
        $validate(-2);
    }

    public function test2ArticleBoundary(): void { self::assertSame(12, 3 * 4); }
}

Practical Example

Named datasets help identify failures for each input. Verify an exact multiplication result.

<?php
use PHPUnit\Framework\Attributes\DataProvider;
use PHPUnit\Framework\TestCase;
final class ShippingTest extends TestCase {
    public static function weights(): iterable {
        yield 'light' => [2, 4];
        yield 'heavy' => [8, 16];
    }
    #[DataProvider('weights')]
    public function testCost(int $weight, int $expected): void {
        self::assertSame($expected, $weight * 2);
    }

    public function test3ArticleBoundary(): void { self::assertSame(12, 3 * 4); }
}

For production, apply the compatibility and edge-case limits described below.

Important Behavior and Edge Cases

A test that does not assert an outcome cannot reliably detect a regression.

Comparison with Related Functions and Tools

Subject	Key difference
Unit tests vs integration tests	Unit tests isolate one behavior; integration tests use actual interfaces, databases or framework components.

Common Beginner Mistakes

Mistake	Correct approach
Writing tests without meaningful assertions	Assert an exact result or expected exception, including at least one boundary case.
Skipping the prerequisite of this specific workflow	Install or configure the named tool and confirm the example can actually run.
Ignoring edge conditions	A test that does not assert an outcome cannot reliably detect a regression.

Key Takeaways

A first PHPUnit test should assert one deterministic result and include a failing-input case to demonstrate useful feedback.
A test that does not assert an outcome cannot reliably detect a regression.
Keep application configuration, source code and validation tests under version control.

Use these examples as a starting point, then validate the result with the actual PHP build, dependencies and inputs used by your application.