Yes as far as Undergraduate Admissions are concerned, IIST does have its own UG Admission Test besides accepting JEE Advanced Rank and Score for Admission Purposes. You can opt for either of them as per your convenience

For more information about IIST Trivandrum and its admission and councelling procedure do follow the link below

https://www.careers360.com/university/indian-institute-of-space-science-and-technology-thiruvananthapuram