What is the govt-recommended method to check chemicals in watermelon?

Food Safety and Standards Authority of India has recommended a cotton test to check if watermelons are contaminated with erythrosine, which adds red colour to foods and beverages. It recommends people to cut the watermelon into two halves and rub a cotton ball in inner succulent parts of the watermelon. The cotton ball rubbed on adulterated watermelon will turn red.