Can someone pliz tell me how accurate r the dna test from walgreens

So I just move from Texas to Illinois with my bf....he's ex gf says that he's the father of her child he doesn't have no kids he wasn't sure if he was so he tested the child without her knowing cuz she wouldn't allow it... he use a DNA test from Walgreens it came out 0% chance but she keeps bugging him that he is n that stresses me so much cuz I want a child with him 😢