code: def test_register_backend_specific_fails_with_unavailable_backend():
      def f_backend_specific(x):
          return x
  
      with pytest.raises(ValueError):
  
          @register_backend_specific(
              "unavailable_backend", f_backend_specific
          )
          def f(x):
              return x
  
file_path: tensorly/tensorly/utils/tests/test_backend_specific.py
imports: import pytest
  import tensorly.utils.backend_specific
  from tensorly.utils.backend_specific import register_backend_specific
label_desc: Use image node_id 8 for calling a global function with example usage: test_register_backend_specific_fails_with_unavailable_backend() and returns: x, x