Unit tests are great if you want to validate the behavior of a single unit of code. By “unit of code” we usually mean a class although it could also be a script.
Everything is explained in the PHPUnit 5.7 documentation.
For unit tests, we strongly encourage you to base your test on the PHPUnit’s TestCase class only.
For instance:
<?php
namespace Tests\Unit\Foo;
use PHPUnit\Framework\TestCase;
class BarTest extends TestCase
{
/* ... */
}
Unit tests should be located into tests/Unit folder and follow the same path as the tested class: if a class is located into src/Core/Foo/Baz, the unit test should be into tests/Unit/Core/Foo/Baz folder.