creating ssh connection in shell script with password

Question

I can log on to a client using a username and password. I know ssh keys are better and more secure, but for now I still want to do this with a password.

[michael@devserver ~]$ ssh -p 3333  -D 3333 testuser@localhost
testuser@localhost's password:
bind: Address already in use
channel_setup_fwd_listener: cannot listen to port: 3333
Could not request local forwarding.

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Last login: Thu Nov 16 17:46:54 2017 from localhost
testuser@mypi:~ $

I would like to do the same but in a script. My attempt is below. When trying however, I am still prompted for a password. I will also later try doing so using ssh keys as shown in my commented out line.

#!/bin/sh
userServer='serveruser'
userClient='clientuser'
passwordServer='serverpassword'
passwordClient='clientpassword'
passwordClient=3333

if echo $passwordClient | ssh -p $port $userClient@localhost | grep ECDSA;  then
# or if keys are used:
# if su -c "ssh -p $port $userClient@localhost" $userServer | grep ECDSA;  then
        echo 'Logon successful'
else
        echo 'Connection refused'
fi