In this section, writing skills are tested on the basis of the responses of the candidates to the questions. Correct vocabulary, grammar and spelling are also tested in the written section.
Since Speaking and Writing section together involve question types that test all the four communicative skills (Speaking, Writing, Reading and Listening), one needs to be absolutely sure about her/his ability of handling all these question types. It always helps to attempt a sample test and understand your comfort level in handling all these question types.