How to use `expect` tool to switch users?

Issue

• How to use expect tool to switch users?
• How can one execute su with password in plain text on the same command line? Is there any way to achieve this using some script?
• When one executes su - root in terminal, it will show like this:

[user@localhost ~]$ su - root
Password: 
[root@localhost ~]# 

• It's required to have some tool/script to work as follows.

[user@localhost ~]$ su - root <someoption> password
[root@localhost ~]#

or

[user@localhost ~]$ su - root | cmd password
[root@localhost ~]#