z = dfs_tree(g5,1)

@test ne(z) == 3 && nv(z) == 4
@test !has_edge(z, 1, 3)

@test topological_sort_by_dfs(g5) == [1, 2, 3, 4]
@test !is_cyclic(g5)
g = DiGraph(3)

add_edge!(g,1,2); add_edge!(g,2,3); add_edge!(g,3,1)

@test is_cyclic(g)
