diff --git a/pina/model/gno.py b/pina/model/gno.py
index 991ca39..3e9af8a 100644
--- a/pina/model/gno.py
+++ b/pina/model/gno.py
@@ -16,6 +16,7 @@ class GraphNeuralKernel(torch.nn.Module):
             n_layers=2,
             internal_n_layers=0,
             internal_layers=None,
+            inner_size=None,
             internal_func=None,
             external_func=None,
             shared_weights=False
@@ -50,6 +51,7 @@ class GraphNeuralKernel(torch.nn.Module):
                 edges_features=edge_features,
                 n_layers=internal_n_layers,
                 layers=internal_layers,
+                inner_size=inner_size,
                 internal_func=internal_func,
                 external_func=external_func)
             self.n_layers = n_layers
@@ -61,6 +63,7 @@ class GraphNeuralKernel(torch.nn.Module):
                     edges_features=edge_features,
                     n_layers=internal_n_layers,
                     layers=internal_layers,
+                    inner_size=inner_size,
                     internal_func=internal_func,
                     external_func=external_func
                 )
@@ -150,6 +153,7 @@ class GNO(KernelNeuralOperator):
                 width=lifting_operator.out_features,
                 edge_features=edge_features,
                 internal_n_layers=internal_n_layers,
+                inner_size=inner_size,
                 internal_layers=internal_layers,
                 external_func=external_func,
                 internal_func=internal_func,
diff --git a/pina/model/layers/graph_integral_kernel.py b/pina/model/layers/graph_integral_kernel.py
index 713b0d7..70d172c 100644
--- a/pina/model/layers/graph_integral_kernel.py
+++ b/pina/model/layers/graph_integral_kernel.py
@@ -10,8 +10,9 @@ class GraphIntegralLayer(MessagePassing):
             self,
             width,
             edges_features,
-            n_layers=0,
+            n_layers=2,
             layers=None,
+            inner_size=None,
             internal_func=None,
             external_func=None
     ):
@@ -28,10 +29,13 @@ class GraphIntegralLayer(MessagePassing):
         from pina.model import FeedForward
         super(GraphIntegralLayer, self).__init__(aggr='mean')
         self.width = width
+        if layers is None and inner_size is None:
+            inner_size = width
         self.dense = FeedForward(input_dimensions=edges_features,
                                  output_dimensions=width ** 2,
                                  n_layers=n_layers,
                                  layers=layers,
+                                 inner_size=inner_size,
                                  func=internal_func)
         self.W = torch.nn.Linear(width, width)
         self.func = external_func()
diff --git a/tests/test_model/test_gno.py b/tests/test_model/test_gno.py
new file mode 100644
index 0000000..e07d845
--- /dev/null
+++ b/tests/test_model/test_gno.py
@@ -0,0 +1,127 @@
+import pytest
+import torch
+from pina.graph import KNNGraph
+from pina.model import GNO
+from torch_geometric.data import Batch
+
+x = [torch.rand(100, 6) for _ in range(10)]
+pos = [torch.rand(100, 3) for _ in range(10)]
+graph = KNNGraph(x=x, pos=pos, build_edge_attr=True, k=6)
+input_ = Batch.from_data_list(graph.data)
+
+
+
+@pytest.mark.parametrize(
+    "shared_weights",
+    [
+        True,
+        False
+    ]
+)
+def test_constructor(shared_weights):
+    lifting_operator = torch.nn.Linear(6, 16)
+    projection_operator = torch.nn.Linear(16, 3)
+    GNO(lifting_operator=lifting_operator,
+        projection_operator=projection_operator,
+        edge_features=3,
+        internal_layers=[16, 16],
+        shared_weights=shared_weights)
+
+    GNO(lifting_operator=lifting_operator,
+        projection_operator=projection_operator,
+        edge_features=3,
+        inner_size=16,
+        internal_n_layers=10,
+        shared_weights=shared_weights)
+
+    int_func = torch.nn.Softplus
+    ext_func = torch.nn.ReLU
+
+    GNO(lifting_operator=lifting_operator,
+        projection_operator=projection_operator,
+        edge_features=3,
+        internal_n_layers=10,
+        shared_weights=shared_weights,
+        internal_func=int_func,
+        external_func=ext_func)
+
+
+@pytest.mark.parametrize(
+    "shared_weights",
+    [
+        True,
+        False
+    ]
+)
+def test_forward_1(shared_weights):
+    lifting_operator = torch.nn.Linear(6, 16)
+    projection_operator = torch.nn.Linear(16, 3)
+    model = GNO(lifting_operator=lifting_operator,
+                projection_operator=projection_operator,
+                edge_features=3,
+                internal_layers=[16, 16],
+                shared_weights=shared_weights)
+    output_ = model(input_)
+    assert output_.shape == torch.Size([1000, 3])
+
+@pytest.mark.parametrize(
+    "shared_weights",
+    [
+        True,
+        False
+    ]
+)
+def test_forward_2(shared_weights):
+    lifting_operator = torch.nn.Linear(6, 16)
+    projection_operator = torch.nn.Linear(16, 3)
+    model = GNO(lifting_operator=lifting_operator,
+                projection_operator=projection_operator,
+                edge_features=3,
+                inner_size=32,
+                internal_n_layers=2,
+                shared_weights=shared_weights)
+    output_ = model(input_)
+    assert output_.shape == torch.Size([1000, 3])
+
+@pytest.mark.parametrize(
+    "shared_weights",
+    [
+        True,
+        False
+    ]
+)
+def test_backward(shared_weights):
+    lifting_operator = torch.nn.Linear(6, 16)
+    projection_operator = torch.nn.Linear(16, 3)
+    model = GNO(lifting_operator=lifting_operator,
+                projection_operator=projection_operator,
+                edge_features=3,
+                internal_layers=[16, 16],
+                shared_weights=shared_weights)
+    input_.x.requires_grad = True
+    output_ = model(input_)
+    l = torch.mean(output_)
+    l.backward()
+    assert input_.x.grad.shape == torch.Size([1000, 6])
+
+@pytest.mark.parametrize(
+    "shared_weights",
+    [
+        True,
+        False
+    ]
+)
+def test_backward_2(shared_weights):
+    lifting_operator = torch.nn.Linear(6, 16)
+    projection_operator = torch.nn.Linear(16, 3)
+    model = GNO(lifting_operator=lifting_operator,
+                projection_operator=projection_operator,
+                edge_features=3,
+                inner_size=32,
+                internal_n_layers=2,
+                shared_weights=shared_weights)
+    input_.x.requires_grad = True
+    output_ = model(input_)
+    l = torch.mean(output_)
+    l.backward()
+    assert input_.x.grad.shape == torch.Size([1000, 6])
\ No newline at end of file