Knowing thyself has always been a never-ending task ... If properly taken, the Riso-Hudson Enneagram Type Indicator (RHETI) will very accurately assess (reliable/valid) your basic personality type.
The Nine Personality Types of the Enneagram
Type 1: The Reformer. The rational, idealistic type.
Type 2: The Helper. The caring, nurturing type.
Type 3: The Motivator. The adaptable, success-oriented type.
Type 4: The Artist. The intuitive, reserved type.
Type 5: The Thinker. The perceptive, cerebral type.
Type 6: The Skeptic. The committed, security-oriented type.
Type 7: The Generalist. The enthusiastic, productive type.
Type 8: The Leader. The powerful, aggressive type.
Type 9: The Peacemaker. The easygoing, accommodating type.
For example: Mine happens to be The Individualist (Type 4, Enneagram typology) - The Sensitive, Withdrawn Type: Expressive, Dramatic, Self-Absorbed, and Temperamental ... At their best, Fours are creative, inspired, honest with themselves, emotionally strong, humane, self-aware, discreet, and self-renewing.
Recognizing Fours: Type Four exemplifies the desire to be ourselves, to be known for who we are, and to know the depths of our own hearts. Of all the types, Fours are most aware of their own emotional states. They notice when they feel upset, anxious, attracted to another person, or some other, more subtle combination of feelings. They pay attention to their different changing emotions and try to determine what their feelings are telling them about themselves, others, and their world. When Fours are more in balance, their exquisite attunement to their inner states enables them to discover deep truths about human nature, to bear compassionate witness to the suffering of others, or to be profoundly honest with themselves about their own motives... By being emotionally honest, and by taking time to see what they really feel about things, they encourage others to look more deeply into themselves.
(Don Richard Riso & Russ Hudson, Discovering Your Personality Type: The Essential Introduction to the Enneagram)