Final answer:
The testament used by the League of Spiritual Discovery was 'The Psychedelic Experience', a guide based on 'The Tibetan Book of the Dead', aimed at facilitating and interpreting LSD trips for spiritual growth.
Step-by-step explanation:
The League of Spiritual Discovery used 'The Psychedelic Experience' as its testament. This book was a manual based on 'The Tibetan Book of the Dead' and was written by Timothy Leary, Ralph Metzner, and Richard Alpert. Its purpose was to serve as a guide for LSD sessions and it drew from the structure and philosophy of 'The Tibetan Book of the Dead' to navigate and interpret the experiences encountered during a psychedelic trip. The League of Spiritual Discovery was an organization that promoted the use of LSD for spiritual growth, and the book was part of their movement advocating for the legal use of psychedelics to explore the mind and spiritual consciousness.