TRUNCATE on table does not take foreign keys in account

CREATE TABLE author (

id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,

name VARCHAR(100) NOT NULL

) ENGINE = InnoDB;

CREATE TABLE book (

id MEDIUMINT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,

title VARCHAR(200) NOT NULL,

author_id SMALLINT UNSIGNED NOT NULL,

CONSTRAINT `fk_book_author`

    FOREIGN KEY (author_id) REFERENCES author (id)

ON DELETE CASCADE

ON UPDATE RESTRICT

) ENGINE = InnoDB;

INSERT INTO author (name) VALUES ('Abdul Alhazred');

INSERT INTO book (title, author_id) VALUES ('Necronomicon', LAST_INSERT_ID());

SELECT * FROM author;

id	name

1	Abdul Alhazred

SELECT * FROM book;

id	title	author_id

1	Necronomicon	1

TRUNCATE TABLE book;

SELECT * FROM author;

id	name

1	Abdul Alhazred

SELECT * FROM book;

id	title	author_id