  A graph $G$ is $H$-free if any subset of $V(G)$ does not induce a subgraph of
$G$ that is isomorphic to $H$. Given a graph $H$, we present sufficient and
necessary conditions for a graph $G$ such that $G/e$ is $H$-free for any edge
$e$ in $E(G)$. Thereafter, we use these conditions to characterize forests,
claw-free, $2K_{2}$-free, $C_{4}$-free, $C_{5}$-free, split, and pseudo-split
graphs.
