diff --git a/core/modules/simpletest/simpletest.module b/core/modules/simpletest/simpletest.module
index 513d46d..45c8c54 100644
--- a/core/modules/simpletest/simpletest.module
+++ b/core/modules/simpletest/simpletest.module
@@ -238,6 +238,32 @@ function simpletest_phpunit_configuration_filepath() {
  *  The results as returned by exec().
  */
 function simpletest_phpunit_run_command(array $unescaped_test_classnames, $phpunit_file) {
+  // Set the up an environment variable containing the database connection so
+  // that functional tests can connect to the database.
+  $db_info = Database::getConnectionInfo();
+  if ($db_info['default']['driver'] == 'sqlite') {
+    $db_url = $db_info['default']['driver'] . '://localhost/' . $db_info['default']['database'];
+  }
+  else {
+    $user = '';
+    if ($db_info['default']['username']) {
+      $user = $db_info['default']['username'];
+      if ($db_info['default']['password']) {
+        $user .= ':' . $db_info['default']['password'];
+      }
+      $user .= '@';
+    }
+
+    $db_url = $db_info['default']['driver'] . '://' . $user . $db_info['default']['host'];
+    if (isset($db_info['default']['port'])) {
+      $db_url .= ':' . $db_info['default']['port'];
+    }
+    $db_url .= '/' . $db_info['default']['database'];
+  }
+  if ($db_info['default']['prefix']['default']) {
+    $db_url .= '#' . $db_info['default']['prefix']['default'];
+  }
+  putenv('SIMPLETEST_DB=' . $db_url);
   $phpunit_bin = simpletest_phpunit_command();
 
   $command = array(
@@ -273,6 +299,7 @@ function simpletest_phpunit_run_command(array $unescaped_test_classnames, $phpun
   // via the simpletest UI.
   $ret = exec(join($command, " "));
   chdir($old_cwd);
+  putenv('SIMPLETEST_DB=');
   return $ret;
 }
 
diff --git a/core/modules/simpletest/src/BrowserTestBase.php b/core/modules/simpletest/src/BrowserTestBase.php
index 443ece8..e457fe4 100644
--- a/core/modules/simpletest/src/BrowserTestBase.php
+++ b/core/modules/simpletest/src/BrowserTestBase.php
@@ -32,6 +32,9 @@
  * Test case for typical Drupal tests.
  *
  * @ingroup testing
+ *
+ * All BrowserTestBase tests must have the @runTestsInSeparateProcesses
+ * annotation to ensure process isolation.
  */
 abstract class BrowserTestBase extends \PHPUnit_Framework_TestCase {
 
@@ -1060,15 +1063,49 @@ private function changeDatabasePrefix() {
 
     // Clone the current connection and replace the current prefix.
     $connection_info = Database::getConnectionInfo('default');
-    Database::renameConnection('default', 'simpletest_original_default');
-    foreach ($connection_info as $target => $value) {
-      // Replace the full table prefix definition to ensure that no table
-      // prefixes of the test runner leak into the test.
-      $connection_info[$target]['prefix'] = array(
-        'default' => $value['prefix']['default'] . $this->databasePrefix,
+    if (is_null($connection_info)) {
+      $db_url = getenv('SIMPLETEST_DB');
+      $info = parse_url($db_url);
+      if (!isset($info['scheme'], $info['host'], $info['path'])) {
+        throw new Wobbly();
+      }
+      $info += array(
+        'user' => '',
+        'pass' => '',
+        'fragment' => '',
+      );
+      if ($info['path'][0] === '/') {
+        $info['path'] = substr($info['path'], 1);
+      }
+      if ($info['scheme'] === 'sqlite' && $info['path'][0] !== '/') {
+        $info['path'] = DRUPAL_ROOT . '/' . $info['path'];
+      }
+      $database = array(
+        'driver' => $info['scheme'],
+        'username' => $info['user'],
+        'password' => $info['pass'],
+        'host' => $info['host'],
+        'database' => $info['path'],
+        'prefix' => array(
+          'default' => $this->databasePrefix,
+        ),
       );
+      if (isset($info['port'])) {
+        $database['port'] = $info['port'];
+      }
+      Database::addConnectionInfo('default', 'default', $database);
+    }
+    else {
+      Database::renameConnection('default', 'simpletest_original_default');
+      foreach ($connection_info as $target => $value) {
+        // Replace the full table prefix definition to ensure that no table
+        // prefixes of the test runner leak into the test.
+        $connection_info[$target]['prefix'] = array(
+          'default' => $value['prefix']['default'] . $this->databasePrefix,
+        );
+      }
+      Database::addConnectionInfo('default', 'default', $connection_info['default']);
     }
-    Database::addConnectionInfo('default', 'default', $connection_info['default']);
   }
 
   /**
diff --git a/core/modules/simpletest/tests/src/Functional/BrowserTestBaseTest.php b/core/modules/simpletest/tests/src/Functional/BrowserTestBaseTest.php
index 6f4c473..99194c5 100755
--- a/core/modules/simpletest/tests/src/Functional/BrowserTestBaseTest.php
+++ b/core/modules/simpletest/tests/src/Functional/BrowserTestBaseTest.php
@@ -14,6 +14,8 @@
  *
  * @group simpletest
  * @group modern
+ *
+ * @runTestsInSeparateProcesses
  */
 class BrowserTestBaseTest extends BrowserTestBase {
 
diff --git a/core/phpunit.xml.dist b/core/phpunit.xml.dist
index 5a9a23f..44bbc33 100644
--- a/core/phpunit.xml.dist
+++ b/core/phpunit.xml.dist
@@ -7,6 +7,7 @@
     <!-- 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://username:password@localhost/databasename#table_prefix"/>
   </php>
   <testsuites>
     <testsuite name="unit">
@@ -18,18 +19,16 @@
       <exclude>./vendor</exclude>
       <!-- Exclude Drush tests. -->
       <exclude>./drush/tests</exclude>
-      <!-- Exclude special-case files from config's test modules. -->
-      <exclude>./modules/config/tests/config_test/src</exclude>
     </testsuite>
     <testsuite name="functional">
-      <directory>./modules/*/tests/src/Functional</directory>
       <directory>./tests/Drupal/FunctionalTests</directory>
+      <directory>./modules/*/tests/src/Functional</directory>
+      <directory>../modules/*/tests/src/Functional</directory>
+      <directory>../sites/*/modules/*/tests/src/Functional</directory>
       <!-- Exclude Composer's vendor directory so we don't run tests there. -->
       <exclude>./vendor</exclude>
       <!-- Exclude Drush tests. -->
       <exclude>./drush/tests</exclude>
-      <!-- Exclude special-case files from config's test modules. -->
-      <exclude>./modules/config/tests/config_test/src</exclude>
     </testsuite>
   </testsuites>
   <listeners>