fix

Author: Nyholm

composer.json

@@ -25,7 +25,8 @@
     },
     "require-dev":  {
         "phpunit/phpunit":                                  "5.0.*|^4.0",
-        "matthiasnoback/symfony-dependency-injection-test": "0.7.*"
+        "matthiasnoback/symfony-dependency-injection-test": "0.7.*",
+        "cache/array-adapter":                              "@stable"
     },
     "suggest":      {
         "cache/*-adapter": "To integrate with a PSR-6 cache"