code: def test_cat(self, backend):
      class TestNet(nn.Module):
          def __init__(self):
              super(TestNet, self).__init__()
  
          def forward(self, x):
              x = torch.cat((x,), axis=1)
              return x
  
      model = TestNet()
      run_compare_torch((1, 3, 16, 16), model, backend=backend)
  
imports: import sys
  from coremltools.converters.mil import testing_reqs
  from coremltools.converters.mil.testing_reqs import *
  from .testing_utils import *
label_desc: Use image node_id 1 for calling the TestConcat obj's underlying member method code with example usage: obj.test_cat(backend) and returns: x