code: def test_gc(self):
      a = Tensor.zeros(4, 4, requires_grad=True)
      b = Tensor.zeros(4, 4, requires_grad=True)
      (a * b).mean().backward()
      assert tensors_allocated() > 0
      del a, b
      assert tensors_allocated() == 0
  
file_path: tinygrad/test/test_gc.py
imports: import gc
  import unittest
  import numpy
  from tinygrad.tensor import Tensor
label_desc: Use image node_id 1 for calling the TestGC obj's underlying member method code with example usage: obj.test_gc() without return types