Today my observation related to oracle roles as follows:

I login in in SQL*Plus as “system” user and gave following commands:
CREATE USER raj IDENTIFIED BY ‘raj’;
GRANT connect,resource TO raj;
CREATE ROLE test IDENTIFIED BY “test”;
GRANT test TO raj;

then I open another instance of SQL*Plus and login as “raj”:
When I gave following command:
CREATE TABLE table1 (col1 VARCHAR2(1));
It create a table for me.

Then I gave following command
SET ROLE ALL;
It generated a error, then I gave following command
SET ROLE test identified by “test”;
then gave following command:
CREATE TABLE table2 (col1 VARCHAR2(1));
It gave me error that I don’t have sufficient Privileges