Symfony WebTestCase "Booting the kernel ... was already booted" client error in CI

By Daniel Zoghalchali·Latchkey

A functional test extending WebTestCase must create its client before booting the kernel any other way. Calling bootKernel() (or self::getContainer() in a way that boots) before createClient() triggers "a kernel has been booted already".

What this error means

A test extending Symfony\Bundle\FrameworkBundle\Test\WebTestCase fails with "LogicException: Booting the kernel before calling ... is not supported, the kernel should only be booted once." or "a kernel has been booted already".

LogicException: Booting the kernel before calling
"Symfony\Bundle\FrameworkBundle\Test\WebTestCase::createClient()" is not supported,
the kernel should only be booted once.

Diagnose it: version, extensions, limits

php -v && php -m | head -30
php -i | grep -E "memory_limit|max_execution_time"
composer check-platform-reqs 2>/dev/null

Common causes

The kernel was booted before createClient()

Calling bootKernel() or fetching the container in a way that boots the kernel before createClient() leaves WebTestCase unable to create its own client.

createClient() called twice in one test

A second createClient() in the same test method tries to boot again after the first client already booted the kernel.

How to fix it

Create the client first, then get the container from it

1. Call static::createClient() as the first kernel interaction.
2. Access services via the client's container ($client->getContainer() or static::getContainer() after createClient).
3. Do not call bootKernel() in a WebTestCase.

$client = static::createClient();
$em = static::getContainer()->get('doctrine')->getManager();
$client->request('GET', '/');

Ensure the kernel is shut down between tests

Let the base tearDown run so each test boots a fresh kernel and no prior boot leaks in.

protected function tearDown(): void
{
    parent::tearDown(); // shuts down the kernel
}

How to prevent it

• Call createClient() before any other kernel interaction in a WebTestCase.
• Fetch services through the test container after creating the client.
• Do not boot the kernel twice in one test method.

Frequently asked questions

Related guides

References

• Composer documentation
• GitHub Actions documentation