How to Run Tests Against an Existing - not testing - Drupal Database - phpunit

Question

I need to run tests again an existing database in Drupal 8.
I already tried to replace default sqllite connection info with the right mysql database's info in phpunit.xml
Here's my phpunit.xml file :
<?xml version="1.0" encoding="UTF-8"?>
<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation="http://schema.phpunit.de/4.1/phpunit.xsd"
bootstrap="test/bootstrap.php"
beStrictAboutTestsThatDoNotTestAnything="true"
beStrictAboutOutputDuringTests="true"
beStrictAboutChangesToGlobalState="true"
strictConfigSchema="false">
<testsuites>
<testsuite name="drupal-composer-project tests">
<directory>./test/</directory>
</testsuite>
</testsuites>
<php>
<!-- Set error reporting to E_ALL. -->
<ini name="error_reporting" value="32767"/>
<!-- Do not limit the amount of memory tests take to run. -->
<ini name="memory_limit" value="-1"/>
<env name="SIMPLETEST_BASE_URL" value="http://localhost"/>
<env name="SIMPLETEST_DB" value="mysql://user:password#mysql/databasename"/>
<env name="BROWSERTEST_OUTPUT_DIRECTORY" value=""/>
</php>
<filter>
<whitelist processUncoveredFilesFromWhitelist="true">
<directory suffix=".php">src</directory>
</whitelist>
</filter>
<listeners>
<listener class="\Drupal\Tests\Listeners\DrupalListener">
</listener>
<!-- The Symfony deprecation listener has to come after the Drupal listener -->
<listener class="Symfony\Bridge\PhpUnit\SymfonyTestsListener">
</listener>
</listeners>
<logging>
<log type="coverage-html" target="../../coverage" charset="UTF-8" yui="true" highlight="true"/>
<log type="coverage-clover" target="../../clover.xml"/>
<log type="coverage-crap4j" target="../../crap4j.xml"/>
</logging>
</phpunit>
When I log database information, I see that a test prefix is added, and this prefix will create tables inside my existing database. How can I make the tests run directly on my own database and tables ?

Answer 1

If you want to run tests on the existing database, you need to use Drupal Test Traits. Here's some introduction text for this testing framework.
But, as #DirkScholten said, you should avoid run tests on the existing database. An exception is running User Acceptance Tests, they need data from the production database in order to simulate an end-user experience. In this case, ensure that you run tests in isolate environment, so as not tests send some mail to the real user or do some changes via API on real servers.
If you just need some custom settings or field on you Drupal's test instance, then a better option is to create your own installation profile and use them in your tests. Here's instructions.
The third option is to use config_installer and doing tests on custom site configuration. From Drupal 8.6 you don't need this module, it's in the Drupal's core.