MAGETWO-69137: upgrading Magento2 Project PHPUnit version to latest

- refactor tests

Author: Igor Melnikov

composer.json

@@ -74,7 +74,6 @@
     },
     "require-dev": {
         "phpunit/phpunit": "~6.2.0",
-        "phpunit/phpunit-dom-assertions": "~2",
         "squizlabs/php_codesniffer": "3.0.1",
         "phpmd/phpmd": "@stable",
         "pdepend/pdepend": "2.5.0",