diff --git a/tests/phpunit/includes/abstract-testcase.php b/tests/phpunit/includes/abstract-testcase.php
index 95a0e0df57..b03d12a097 100644
--- a/tests/phpunit/includes/abstract-testcase.php
+++ b/tests/phpunit/includes/abstract-testcase.php
@@ -387,12 +387,9 @@ abstract class WP_UnitTestCase_Base extends PHPUnit_Adapter_TestCase {
 	public static function flush_cache() {
 		global $wp_object_cache;
 
-		$wp_object_cache->group_ops      = array();
-		$wp_object_cache->stats          = array();
-		$wp_object_cache->memcache_debug = array();
-		$wp_object_cache->cache          = array();
+		wp_cache_flush_runtime();
 
-		if ( method_exists( $wp_object_cache, '__remoteset' ) ) {
+		if ( is_object( $wp_object_cache ) && method_exists( $wp_object_cache, '__remoteset' ) ) {
 			$wp_object_cache->__remoteset();
 		}
 
diff --git a/tests/phpunit/includes/object-cache.php b/tests/phpunit/includes/object-cache.php
index f9e2c4693e..2bea171f19 100644
--- a/tests/phpunit/includes/object-cache.php
+++ b/tests/phpunit/includes/object-cache.php
@@ -325,12 +325,23 @@ function wp_cache_flush( $delay = 0 ) {
 function wp_cache_supports( $feature ) {
 	switch ( $feature ) {
 		case 'get_multiple':
+		case 'flush_runtime':
 			return true;
 		default:
 			return false;
 	}
 }
 
+/**
+ * Removes all cache items from the in-memory runtime cache.
+ *
+ * @return bool True on success, false on failure.
+ */
+function wp_cache_flush_runtime() {
+	global $wp_object_cache;
+	return $wp_object_cache->flush_runtime();
+}
+
 /**
  * Retrieves object from cache.
  *
@@ -1412,6 +1423,17 @@ class WP_Object_Cache {
 		return $result;
 	}
 
+	/**
+	 * Clears the in-memory cache of all data leaving the external cache untouched.
+	 *
+	 * @return bool Always returns true.
+	 */
+	public function flush_runtime() {
+		$this->cache = array();
+
+		return true;
+	}
+
 	/**
 	 * Retrieves object from cache.
 	 *