Add test coverage report in strict mode

Add ability to generate test coverage report in strict mode.

composer.json

@@ -31,6 +31,7 @@
     "scripts": {
         "test": "phpunit",
         "test-cov": "@php -dpcov.enabled=1 -dpcov.directory=. ./vendor/composer/bin/phpunit --coverage-html=.coverage/html",
+        "test-cov-strict": "@php -dpcov.enabled=1 -dpcov.directory=. ./vendor/composer/bin/phpunit --coverage-html=.coverage/html --strict-coverage",
         "php-cs-fixer": "php-cs-fixer"
     }
 }