Testing Wordpress plugins with PHPUnit

I've been working on Wordpress plugins lately, and the amount of legacy code is phenomenal. To cope with that, here's a recipe I use for making little islands of sanity:

1. Install prerequisites

   1. composer: I used brew install composer.
   2. PHPUnit composer require --dev phpunit/phpunit ^11

2. Add a test script in composer.json

   {
       "scripts": {
           "test": "phpunit tests"
       },
       "require-dev": {
           "phpunit/phpunit": "^11"
       }
   }
   

3. Run tests on a file change with entr.

   find . | entr -c composer run test
   

4. TDD new pieces of code before embedding them in legacy code.

   <?php
   declare(strict_types=1);
   class Klass {
       public function something($val): bool {
           return $val;
       }
   }
   ?>
   

   <?php
   declare(strict_types=1);
   use PHPUnit\Framework\TestCase;
   
   final class KlassTest extends TestCase {
       private $klass;
   
       protected function setUp(): void
       {
           $this->klass = new Klass();
       }
   
       public function testOne(): void {
           $this->assertFalse($this->klass->something(false));
           $this->assertTrue($this->klass->something(true));
       }
   }
   ?>
   

5. Enjoy the tranquility of making changes to tested code. 😌