Install codesniffer

composer.json

@@ -42,9 +42,10 @@
     "zendframework/zend-diactoros": "1.4.1"
   },
   "require-dev": {
+    "ext-pdo": "*",
     "phpunit/dbunit": "^2.0",
     "phpunit/phpunit": "^4.0",
-    "ext-pdo": "*"
+    "squizlabs/php_codesniffer": "3.4.2"
   },
   "autoload": {
     "psr-4": {

composer.lock

@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "4e7d1fa77dfae365ac340e54ddd9ae6c",
+    "content-hash": "c1b6812ceff4ba052c142547de9d209a",
     "packages": [
         {
             "name": "doctrine/annotations",
@@ -3021,6 +3021,57 @@
             "homepage": "https://github.com/sebastianbergmann/version",
             "time": "2015-06-21T13:59:46+00:00"
         },
+        {
+            "name": "squizlabs/php_codesniffer",
+            "version": "3.4.2",
+            "source": {
+                "type": "git",
+                "url": "https://github.com/squizlabs/PHP_CodeSniffer.git",
+                "reference": "b8a7362af1cc1aadb5bd36c3defc4dda2cf5f0a8"
+            },
+            "dist": {
+                "type": "zip",
+                "url": "https://api.github.com/repos/squizlabs/PHP_CodeSniffer/zipball/b8a7362af1cc1aadb5bd36c3defc4dda2cf5f0a8",
+                "reference": "b8a7362af1cc1aadb5bd36c3defc4dda2cf5f0a8",
+                "shasum": ""
+            },
+            "require": {
+                "ext-simplexml": "*",
+                "ext-tokenizer": "*",
+                "ext-xmlwriter": "*",
+                "php": ">=5.4.0"
+            },
+            "require-dev": {
+                "phpunit/phpunit": "^4.0 || ^5.0 || ^6.0 || ^7.0"
+            },
+            "bin": [
+                "bin/phpcs",
+                "bin/phpcbf"
+            ],
+            "type": "library",
+            "extra": {
+                "branch-alias": {
+                    "dev-master": "3.x-dev"
+                }
+            },
+            "notification-url": "https://packagist.org/downloads/",
+            "license": [
+                "BSD-3-Clause"
+            ],
+            "authors": [
+                {
+                    "name": "Greg Sherwood",
+                    "role": "lead"
+                }
+            ],
+            "description": "PHP_CodeSniffer tokenizes PHP, JavaScript and CSS files and detects violations of a defined set of coding standards.",
+            "homepage": "https://github.com/squizlabs/PHP_CodeSniffer",
+            "keywords": [
+                "phpcs",
+                "standards"
+            ],
+            "time": "2019-04-10T23:49:02+00:00"
+        },
         {
             "name": "symfony/yaml",
             "version": "v3.4.24",