code: def test_fiedler_vector_tracemin_unknown():
      """Test that "tracemin_unknown" raises an exception."""
      pytest.importorskip("scipy")
      G = nx.barbell_graph(5, 4)
      L = nx.laplacian_matrix(G)
      X = np.asarray(np.random.normal(size=(1, L.shape[0]))).T
      with pytest.raises(
          nx.NetworkXError, match="Unknown linear system solver"
      ):
          nx.linalg.algebraicconnectivity._tracemin_fiedler(
              L,
              X,
              normalized=False,
              tol=1e-8,
              method="tracemin_unknown",
          )
  
imports: from math import sqrt
  import pytest
  import networkx
label_desc: Use image node_id 4 for calling a global function with example usage: test_fiedler_vector_tracemin_unknown() without return types