code: def test_subgraph_2(n=10):
      x = nr.randn(n, 2)
      G = knn(x, 5)
      valid = np.zeros(n)
      valid[: n // 2] = 1
      assert G.subgraph(valid).edges.max() < n / 2
  
imports: import numpy
  import numpy.random
  from numpy.testing import assert_almost_equal, assert_array_almost_equal, assert_array_equal
  from ..graph import WeightedGraph, complete_graph, concatenate_graphs, eps_nn, knn, mst, wgraph_from_3d_grid, wgraph_from_adjacency, wgraph_from_coo_matrix
label_desc: Use image node_id 42 for calling a global function with example usage: test_subgraph_2(n) without return types