look at the phpunit code to see how to load the configuration file of phpunit. When you call the file_exsits () function, add a backslash "\" in front of it. The code is as follows:

if (isset($this->arguments["configuration"]) &&
            \is_dir($this->arguments["configuration"])) {
            $configurationFile = $this->arguments["configuration"] . "/phpunit.xml";

            if (\file_exists($configurationFile)) {
                $this->arguments["configuration"] = \realpath(
                    $configurationFile
                );
            } elseif (\file_exists($configurationFile . ".dist")) {
                $this->arguments["configuration"] = \realpath(
                    $configurationFile . ".dist"
                );
            }
        } elseif (!isset($this->arguments["configuration"]) &&
            $this->arguments["useDefaultConfiguration"]) {
            if (\file_exists("phpunit.xml")) {
                $this->arguments["configuration"] = \realpath("phpunit.xml");
            } elseif (\file_exists("phpunit.xml.dist")) {
                $this->arguments["configuration"] = \realpath(
                    "phpunit.xml.dist"
                );
            }
        }

if (\ file_exists ("phpunit.xml")) what does this mean? Can you specify to find the "phpunit.xml" file from the root directory? ;