User without a password - how can one login into that account from a non-root account

I have just started to use Scientific Linux (7.0) (although I assume this question might be distribution neutral..). The kernel version is 3.10.0-123.20.1.el7.x86_64. Coming back to my question. I switched to root account and from there created an new user account test-account using the command adduser test-account. It didn't prompt me for a password neither did I use the option to provide passwor

[takahiroki]

su からでしか入れないアカウントというものも作成しうる。普通に作成して、パスワードを設定しなければ、大体そうなる。