Add missing tests directory.

Author: mitchdav

.github/workflows/run-tests.yml

@@ -40,4 +40,4 @@ jobs:
           composer update --${{ matrix.dependency-version }} --prefer-dist --no-interaction --no-suggest
 
       - name: Execute tests
-        run: vendor/bin/phpunit
+        run: vendor/bin/phpunit tests

composer.json

@@ -19,7 +19,7 @@
     }
   ],
   "scripts": {
-    "test": "phpunit"
+    "test": "phpunit tests"
   },
   "autoload": {
     "psr-4": {