dragons_test are artificial, generated form the same ground truth model,
but with sometimes different data distridution.
a data frame with 2000 rows and 8 columns
Values are generated in a way to: - have nonlinearity in year_of_birth and height - have concept drift in the test set
year_of_birth - year in which the dragon was born. Negative year means year BC, eg: -1200 = 1201 BC
year_of_discovery - year in which the dragon was found.
height - height of the dragon in yards.
weight - weight of the dragon in tons.
scars - number of scars.
colour - colour of the dragon.
number_of_lost_teeth - number of teeth that the dragon lost.
life_length - life length of the dragon.