php-codeigniter-tdd

PHP CodeIgniter TDD

Red-green-refactor for CodeIgniter 4 (CI4), with the framework-specific parts: which trait wires up the database per test, why CI4 insists on a separate tests database group, and how to assert against a full HTTP request/response cycle instead of calling a controller method directly.

For the generic RED-GREEN-REFACTOR cycle, see skills/test-driven-development/. This skill covers what's specific to CI4 on top of that cycle.

Base class and traits

Every CI4 test extends CodeIgniter\Test\CIUnitTestCase. Add CodeIgniter\Test\DatabaseTestTrait only when the test actually touches the database — it adds real per-test cost (migration/refresh/seed), so a pure unit test (a value object, a calculator) should not use it.

use CodeIgniter\Test\CIUnitTestCase;
use CodeIgniter\Test\DatabaseTestTrait;

final class ReservationModelTest extends CIUnitTestCase
{
    use DatabaseTestTrait;

    protected $refresh = true;
    protected $seed    = 'ReservationSeeder';

    public function testCreateRejectsCheckOutBeforeCheckIn(): void
    {
        $model = new \App\Models\ReservationModel();

        $result = $model->insert([
            'guest_id'  => 1,
            'check_in'  => '2026-06-10',
            'check_out' => '2026-06-05',
        ]);

        $this->assertFalse($result);
        $this->assertArrayHasKey('check_out', $model->errors());
    }
}

The tests database group — not optional, not decorative

DatabaseTestTrait requires a dedicated tests connection group defined in app/Config/Database.php, separate from default. Per the CI4 user guide, this exists specifically so database tests never touch "your other data" — the trait's $migrate/$refresh/$seed behavior runs migrations, seeds, and (with $refresh = true) rolls back or re-migrates the schema, against whichever connection the tests group actually points to.

// app/Config/Database.php
public array $tests = [
    'DSN'      => '',
    'hostname'  => 'localhost',
    'database'  => 'app_test',        // a real, separate database
    'username'  => 'root',
    'password'  => '',
    'DBDriver'  => 'MySQLi',
    'port'      => 3306,
];