In this paper, we study learning and testing decision tree of size and depth that are significantly smaller than the number of attributes $n$. Our main result addresses the problem of poly$(n,1/ε)$ time algorithms with poly$(s,1/ε)$ query complexity (independent of $n$) that distinguish between functions that are decision trees of size $s$ from functions that are $ε$-far from any decision tree of size $φ(s,1/ε)$, for some function $φ> s$. The best known result is the recent one that follows from Blank, Lange and Tan,~\cite{BlancLT20}, that gives $φ(s,1/ε)=2^{O((\log^3s)/ε^3)}$. In this paper, we give a new algorithm that achieves $φ(s,1/ε)=2^{O(\log^2 (s/ε))}$. Moreover, we study the testability of depth-$d$ decision tree and give a {\it distribution free} tester that distinguishes between depth-$d$ decision tree and functions that are $ε$-far from depth-$d^2$ decision tree. In particular, for decision trees of size $s$, the above result holds in the distribution-free model when the tree depth is $O(\log(s/ε))$. We also give other new results in learning and testing of size-$s$ decision trees and depth-$d$ decision trees that follow from results in the literature and some results we prove in this paper.