code: def test_warp_by_flow_forward_backward(shape, seed, ctx, func_name):
      N, C, H, W = shape
      rng = np.random.RandomState(seed)
      data = rng.randn(N, C, H, W).astype(np.float32)
      flow = rng.randn(N, 2, H, W).astype(np.float32)
      function_tester(
          rng,
          F.warp_by_flow,
          warp_by_flow,
          [data, flow],
          ctx=ctx,
          func_name=func_name,
          func_args=[],
          atol_b=1e-2,
      )
  
imports: import pytest
  import numpy
  import nnabla.functions
  from nbla_test_utils import list_context, function_tester
label_desc: Use image node_id 2 for calling a global function with example usage: test_warp_by_flow_forward_backward(shape, seed, ctx, func_name) without return types