Document how to run integration tests locally

I am also replacing the commented out connection parameters in
phpunit.xml.dist with a link to this paragraph because they have
diverged from the one we use in the CI since f88dc28.

docs/en/reference/testing.rst

@@ -62,6 +62,31 @@ multiple concurrent database connections, transactions, locking, performance-rel
 In such cases, it is still important that a pull request fixing the issues is accompanied by a free-form reproducer
 that demonstrates the issue being fixed.
 
+Running Integration Tests locally
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The default ``phpunit.xml.dist`` configuration file is set up to run the
+integration tests against SQLite, but you need to enable the extension
+``pdo_sqlite`` in your PHP configuration.
+
+To run the integration tests against another platform, you can use one
+of the configuration files used in our continuous integration setup.
+Those are stored under ``ci/github/``.
+
+For instance, to run tests against MySQL using the PDO driver, you
+should spin up a MySQL server, enable the ``pdo_mysql`` extension, and
+then run the following command:
+
+.. code-block:: console
+
+    $ phpunit -c ci/github/pdo_mysql.xml
+
+We do not currently have specific instructions on how to run a Database
+server, but we do recommend Docker as a convenient way to do so.
+We do not recommend running against a particular version of the chosen
+RDBMS either, as long as you pick one of the
+:doc:`officially supported versions <reference/platforms>`.
+
 Recommendations on Writing Tests
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

phpunit.xml.dist

@@ -22,24 +22,11 @@
     <php>
         <ini name="error_reporting" value="-1" />
 
-        <!-- Test connection parameters -->
-        <!-- Uncomment, otherwise SQLite runs
-        <var name="db_driver" value="pdo_mysql"/>
-        <var name="db_host" value="localhost" />
-        <var name="db_port" value="3306"/>
-        <var name="db_user" value="root" />
-        <var name="db_password" value="" />
-        <var name="db_dbname" value="doctrine_tests" />
+        <!--
+            By default, the tests are run against SQLite.
+            If you want to run them against another DBMS,
+            see https://www.doctrine-project.org/projects/doctrine-dbal/en/stable/reference/testing.html#running-integration-tests-locally
         -->
-        <!--<var name="db_event_subscribers" value="Doctrine\DBAL\Event\Listeners\OracleSessionInit">-->
-
-        <!-- Privileged user connection parameters. Used to create and drop the test database -->
-        <var name="tmpdb_driver" value="pdo_mysql"/>
-        <var name="tmpdb_host" value="localhost" />
-        <var name="tmpdb_port" value="3306"/>
-        <var name="tmpdb_user" value="root" />
-        <var name="tmpdb_password" value="" />
-        <var name="tmpdb_dbname" value="doctrine_tests_tmp" />
     </php>
 
     <testsuites>