Feature vs Unit Tests: The Difference

In this lesson, let's talk about Unit Tests versus Feature Tests.

A unit is some internal piece of code in your application: usually a function or a class. So, the purpose of Unit tests is to test precisely those units, without loading the full page routes or API endpoints.

Unit tests usually don't use the full feature but instead, test that some internal method returns correct data.

Let me show you a practical example.

New Feature: Service Class

For this example, we want to show additional prices in Euro in the table.

To show the price in Euro, there is a converter. Imagine a CurrencyService class in the App\Services directory. In the service, there is a function to convert the price.

app/Services/CurrencyService.php:

namespace App\Services;
 
class CurrencyService
{
    const RATES = [
        'usd' => [
            'eur' => 0.98
        ],
    ];
 
    public function convert(float $amount, string $currencyFrom, string $currencyTo): float
    {
        $rate = self::RATES[$currencyFrom][$currencyTo] ?? 0;
 
        return round($amount * $rate, 2);
    }
}

For simplicity, we just fake the conversion rate as a constant. In the real world, of course, there will be...