[test] add shard util tests

tests/test_shardformer/test_shard_utils.py

@@ -0,0 +1,27 @@
+import torch
+import torch.nn as nn
+
+from colossalai.shardformer.shard.utils import set_tensors_to_none
+
+
+class Net(nn.Module):
+
+    def __init__(self) -> None:
+        super().__init__()
+        self.layers = nn.Sequential(nn.Linear(1, 2), nn.Linear(2, 3))
+        self.out = nn.Linear(3, 1)
+
+
+def test_release_layer():
+    orig_cuda_allocated = torch.cuda.memory_allocated()
+    model = Net().cuda()
+    set_tensors_to_none(model, exclude={model.layers[0]})
+    assert model.layers[1].weight is None
+    assert model.layers[1].bias is None
+    assert model.out.weight is None
+    assert model.out.bias is None
+    set_tensors_to_none(model)
+    assert model.layers[0].weight is None
+    assert model.layers[0].bias is None
+    assert len(list(model.parameters())) == 0
+    assert torch.cuda.memory_allocated() == orig_cuda_allocated