Symfony PHPUnit self::$kernel is null in second test

Question

I am trying to create a PHPunit test accessing services from the container in symfony. To do so I call self::bootKernel in setUpBeforeClass. In the first test, the self::$kernel is ok, but the second test self::$kernel is null.

This is a simple test to check it:

<?php

namespace App\Tests;

use Symfony\Bundle\FrameworkBundle\Test\WebTestCase;

class KernelTest extends WebTestCase
{
    public static function setUpBeforeClass(): void
    {
        self::bootKernel();
    }

    public function testMethod1(){
        $this->assertNotNull(self::$kernel);
    }

    public function testMethod2(){
        $this->assertNotNull(self::$kernel);
    }
}

This produces the following output:

$ bin/phpunit tests/KernelTest.php 
PHPUnit 7.5.18 by Sebastian Bergmann and contributors.

Notice: Undefined index: warnings in /app/vendor/phpunit/phpunit/src/TextUI/TestRunner.php on line 334

Warning: Invalid argument supplied for foreach() in /app/vendor/phpunit/phpunit/src/TextUI/TestRunner.php on line 334

Testing App\Tests\KernelTest
.F                                                                  2 / 2 (100%)

Time: 58 ms, Memory: 16.00 MB

There was 1 failure:

1) App\Tests\KernelTest::testMethod2
Failed asserting that null is not null.

/app/tests/KernelTest.php:19

FAILURES!
Tests: 2, Assertions: 2, Failures: 1.

As you can see, the second test fails the assertion.

This is the version that I am running of phpunit:

phpunit/phpunit                     8.5.2      The PHP Unit Testing framework.
symfony/phpunit-bridge              v5.0.2     Symfony PHPUnit Bridge

What I am doing wrong? Should I boot kernel in each test? I would like to boot it only once.

Answer 1

Just have a look at the definition of the WebTestCase, for example through GitHub: in its tearDown method, the parent tearDown of the KernelTestCase (see GitHub once more) is called, and this forces a shutdown of the kernel. As tearDown is called after each invididual test, booting the kernel once before all other tests does not help.

Symfony's own documentation boots the kernel in setUp (happening right before each individual test case), so that looks reasonable to me.

If you fear performance issues, keep in mind that such integration tests should not be used everywhere. By following the usual testing pyramid, you should have lots of unit tests (testing small parts of your code in isolation), less tests for coupled classes (where you could mock depending parts), and only a few test cases covering the whole system