PHP Unit Testing (PHPUnit)

Unit testing is like checking each LEGO brick on its own to make sure it is not broken before building the castle. Small automatic tests confirm that every piece of code does its job.

In this page:

Introduction to Unit Testing
Writing your First Test
Test Assertions
Testing Setup and Teardown
Running PHPUnit

Syntax

php

use PHPUnit\Framework\TestCase;

class ClassNameTest extends TestCase {
    public function testSomething() {
        $this->assertEquals(expected, actual);
    }
}

Introduction to Unit Testing

Unit testing checks small, isolated pieces of code -- typically a single function or method -- in automated fashion, catching regressions the moment a change breaks something instead of during manual QA weeks later.

Example: Introduction to Unit Testing

php

<?php
function add($a, $b) {
    return $a + $b;
}
// A unit test would automatically check: add(2, 3) === 5
var_dump(add(2, 3) === 5);
?>

Writing your First Test

A PHPUnit test class extends TestCase and defines methods (conventionally prefixed with test) that each exercise one specific behavior and assert what the correct outcome should be.

Example: Writing your First Test

php

<?php
// use PHPUnit\Framework\TestCase;
// class MathTest extends TestCase {
//     public function testAddition() {
//         $this->assertEquals(5, add(2, 3));
//     }
// }
echo "A PHPUnit test class extends TestCase";
?>

Test Assertions

PHPUnit ships dozens of purpose-built assertions -- assertEquals, assertArrayHasKey, assertStringContainsString -- that produce far more informative failure messages than a bare if-check ever could.

Example: Test Assertions

php

<?php
// $this->assertEquals(5, add(2, 3));
// $this->assertArrayHasKey('id', $user);
// $this->assertStringContainsString('Alice', $greeting);
echo "PHPUnit assertions produce clear failure messages";
?>

Testing Setup and Teardown

setUp() runs before every single test method to prepare fresh fixtures (like a clean database connection), and tearDown() runs after each one to clean up, keeping tests fully isolated from each other.

Example: Testing Setup and Teardown

php

<?php
// protected function setUp(): void { $this->db = new SQLite3(':memory:'); }
// protected function tearDown(): void { $this->db->close(); }
echo "setUp runs before, tearDown runs after each test method";
?>

Running PHPUnit

Running phpunit from the terminal scans your test directory for files matching *Test.php and executes every test method it finds, reporting a pass/fail summary for the whole suite in one command.

Example: Running PHPUnit

php

<?php
// Run in terminal: phpunit
echo "Scans for *Test.php files and reports a pass/fail summary";
?>

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