测试用例添加 setUp（）方法之后执行错误？

ProductTest文件

<?php

namespace Tests\Unit;

use Tests\TestCase;
use Illuminate\Foundation\Testing\WithFaker;
use Illuminate\Foundation\Testing\RefreshDatabase;
use App\Product;

class ProductTest extends TestCase
{
    public $product;

    public function setUp()
    {
        parent::setUp();
        $this->product = new Product('xiaocai', 59);
    }
    /**
     * A basic unit test example.
     *
     * @return void
     */
    public function testName()
    {
        $this->assertEquals('xiaocai', $this->product->name());
    }

    public function testPrice()
    {
        $this->assertEquals(59, $this->product->price());
    }
}

执行./vendor/bin/phpunit --filter ProductTest之后出现如下错误

$ ./vendor/bin/phpunit --filter ProductTest
PHP Fatal error:  Declaration of Tests\Unit\ProductTest::setUp() must be compatible with Illuminate\Foundation\Testing\TestCase::setUp(): void in D:\study\XAMPP\htdocs\laravel-phpunit\tests\Unit\ProductTest.php on line 33

Fatal error: Declaration of Tests\Unit\ProductTest::setUp() must be compatible with Illuminate\Foundation\Testing\TestCase::setUp(): void in D:\study\XAMPP\htdocs\laravel-phpunit\tests\Unit\ProductTest.php on line 33