require.ErrorContains(t, tree.Add(testNode(0, 0, "user: b")), "already built")
require.ErrorContains(t, tree.Add(testNode(1, 0, "a b")), "child that is not built")
require.ErrorContains(t, tree.Add(testNode(0, 0, "user: b")), "already built")
require.ErrorContains(t, tree.Add(testNode(1, 0, "a b")), "child that is not built")