Add composer script to run tests in proper isolation. That's necessary as we're messing with globals by design in this library and its tests.

Author: Crell

composer.json

@@ -25,5 +25,8 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^7.0"
+    },
+    "scripts": {
+        "test": "vendor/bin/phpunit --process-isolation --bootstrap vendor/autoload.php tests/FlexBridgeTest.php"
     }
 }