Fix compatibility with PHPUnit 8 (#21)

The method's signature changed in sebastianbergmann/phpunit@f5e5add

Author: jderusse

.travis.yml

@@ -52,6 +52,7 @@ before_install:
     - if [[ $COVERAGE != true ]]; then phpenv config-rm xdebug.ini || true; fi
     - if ! [ -z "$STABILITY" ]; then composer config minimum-stability ${STABILITY}; fi;
     - if ! [ -v "$DEPENDENCIES" ]; then composer require --no-update ${DEPENDENCIES}; fi;
+    - echo "memory_limit=2G" >> ~/.phpenv/versions/$(phpenv version-name)/etc/conf.d/travis.ini
 
 install:
     # To be removed when this issue will be resolved: https://github.com/composer/composer/issues/5355

src/BaseBundleTestCase.php

@@ -74,8 +74,10 @@ protected function createKernel()
 
     /**
      * Shuts the kernel down if it was used in the test.
+     *
+     * @after
      */
-    private function ensureKernelShutdown()
+    public function ensureKernelShutdown()
     {
         if (null !== $this->kernel) {
             $container = $this->kernel->getContainer();
@@ -86,14 +88,6 @@ private function ensureKernelShutdown()
         }
     }
 
-    /**
-     * Clean up Kernel usage in this test.
-     */
-    protected function tearDown()
-    {
-        $this->ensureKernelShutdown();
-    }
-
     /**
      * @param CompilerPassInterface $compilerPass
      */