added phpunit tests

Author: Alexsey-VR

Makefile

@@ -6,3 +6,6 @@ validate:
 
 lint:
 	composer exec --verbose phpcs -- --standard=PSR12 src bin
+
+test:
+	composer exec --verbose phpunit tests

composer.json

@@ -6,7 +6,8 @@
         "docopt/docopt": "^1.0.6"
     },
     "require-dev": {
-        "squizlabs/php_codesniffer": "^3.7"
+        "squizlabs/php_codesniffer": "^3.7",
+        "phpunit/phpunit": "^12.2.5"
     },
     "license": "MIT",
     "autoload": {