Installing PHPUnit

PHPUnit is a development test runner installed as a Composer development dependency. A project-local runner avoids mismatches with a globally installed version.

What It Does

Install and check the test runner. Create a minimal test class in the tests directory.

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

Install and check the test runner.

composer require --dev phpunit/phpunit
vendor/bin/phpunit --version

Example 2: Another Case

Create a minimal test class in the tests directory.

<?php
use PHPUnit\Framework\TestCase;
final class BasicTest extends TestCase {
    public function testMath(): void { self::assertSame(4, 2 + 2); }
}

Practical Example

Run the complete suite and one selected test.

vendor/bin/phpunit tests
vendor/bin/phpunit --filter=testMath

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

Important Behavior and Edge Cases

Choose a PHPUnit release compatible with the PHP versions your project supports.

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	Choose a PHPUnit release compatible with the PHP versions your project supports.

Key Takeaways

PHPUnit is a development test runner installed as a Composer development dependency. A project-local runner avoids mismatches with a globally installed version.
Choose a PHPUnit release compatible with the PHP versions your project supports.
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.