What is Yazidism, and what are the books that discuss it?

The Yazidis are a sect that emerged in the year 132 AH after the collapse of the Umayyad state. Initially, it was a political movement, then it deviated to sanctify Yazid ibn Abi Sufyan and Iblis (Malak Tawus). Among their beliefs are: denouncing the cursing of Yazid and Iblis. They have their own sacred book called "The Black Book". Their Shahada (testimony of faith) is: "I bear witness that the one God is Sultan Yazid, the beloved of God." They fast three days coinciding with Yazid's birthday, and they perform one prayer a year on the night of mid-Sha'ban. Polygyny is permitted up to six wives. They prohibit the color blue, lettuce, cabbage, shaving the mustache, reading, and writing. They believe in incarnation (hulul) and unification (ittihad) and venerate shrines. They respect Christianity and baptize their children. This sect exists in Syria, Turkey, Iran, Russia, Iraq, Lebanon, and some European countries. There are many books that discuss them.