Enable PHPStan in PHPUnit

composer.json.patch

diff --git a/composer.json b/composer.json
index d1d0595e5..6b04dc677 100644
--- a/composer.json
+++ b/composer.json
@@ -47,7 +47,8 @@
         "sebastian/version": "^2.0.1"
     },
     "require-dev": {
-        "ext-PDO": "*"
+        "ext-PDO": "*",
+        "phpstan/phpstan": "^0.9"
     },
     "config": {
         "platform": {
@@ -79,6 +80,10 @@
             "tests/_files/NamespaceCoveredFunction.php"
         ]
     },
+    "scripts": {
+        "phpstan": "phpstan analyse --level=0 -c phpstan.neon src",
+        "phpstan-tests": "phpstan analyse --level=0 -c phpstan-tests.neon tests"
+    },
     "extra": {
         "branch-alias": {
             "dev-master": "7.1-dev"