nginx conditional proxy pass

try this:

server {
    listen 80 default;
    server_name test.local;

    location / {
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $remote_addr;
        proxy_set_header Host $http_host;

        if ($request_body ~* ^(.*)\.test) {
            proxy_pass http://www.google.de;
            break;
        }

        root /srv/http;
    }

}