' and \ characters in passwords

I found that \ characters needs not to be quoted in password strings

create role test1 password '\'

is OK.
I havent found any mention of this behaviour in docs.
Where this is documented ?

I created role

create role test2 password ''''

Trying to login using password ' causes error from my ODBC client:

Connectivity error: FATAL: password authentication failed for user "test2"

ODBC and postgres logs do not show anything about this issue. How can I find
which is wrong ?

Is

create role test2 password ''''

legal way to set password to ' character ?

Andrus.