public void DFS1()
{
var dfs = new DFS <int>();
var tree = BuildBunchOfIntNodes();
Assert.False(dfs.Contains(tree, 1));
Assert.False(dfs.Contains(null, 1));
Assert.True(dfs.Contains(tree, 10));
Assert.True(dfs.Contains(tree, 45));
Assert.True(dfs.Contains(tree, 25));
Assert.False(dfs.Contains(tree, 125));
}