Why is India not trying Arshdeep Singh in Tests?

https://preview.redd.it/d48in1n62u6e1.jpg?width=1080&format=pjpg&auto=webp&s=dcfeb8bc9c05b495a9f53b0b0af9970e7871a666 Is he being earmarked purely for T20s? India has never found a Zaheer Khan replacement & he is doing pretty well, I believe he has even played county cricket in England. India lacks a good left arm pacer who can swing the ball really well in tests, and he is an answer, he can also support Boom in opening spells. Forgive me please if I'm being ignorant as I don't avidly follow domestic cricket!