Testing Exception Classes

Let's talk about what happens if some Exceptions appear, and you want to test if a particular Exception is successfully thrown in your tests.

Exception Example 1

Imagine a scenario where, in a Service, you throw an Exception. It may be your custom Exception or a Laravel Exception like ModelNotFound.

In this example, we throw our custom Exception if the currency rate doesn't exist.

namespace App\Services;
 
use Illuminate\Support\Arr;
use App\Exceptions\CurrencyRateNotFoundException;
 
class CurrencyService
{
    const RATES = [
        'usd' => [
            'eur' => 0.98
        ],
    ];
 
    public function convert(float $amount, string $currencyFrom, string $currencyTo): float
    {
        if (! Arr::exists(self::RATES, $currencyFrom)) {
            throw new CurrencyRateNotFoundException('Currency rate not found'); 
        }
 
        $rate = self::RATES[$currencyFrom][$currencyTo] ?? 0;
 
        return round($amount * $rate, 2);
    }
}

Another example: in the Model, you have an attribute to show a converted price, but in case of an Exception, you log, alert, or do something else.

use App\Services\CurrencyService;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\Casts\Attribute;
use App\Exceptions\CurrencyRateNotFoundException;
use Illuminate\Database\Eloquent\Factories\HasFactory;
 
class Product extends Model
{
    protected $fillable = [
        'name',
        'price',
    ];
 
    protected function eurPrice(): Attribute
    {
        return Attribute::make(
            get: function () {
                try {
                    return (new CurrencyService())->convert($this->price, 'usd', 'eur');
                } catch (CurrencyRateNotFoundException $e) {
                    // Log something, alert someone
                }
            },
        );
    }
}

The Test

This test is going to be a Unit test, not a Feature. We're not testing...