code: def test_mix_use_context(self):
      # See cupy/cupy#5143
      s1 = cuda.Stream()
      s2 = cuda.Stream()
      s3 = cuda.Stream()
      assert cuda.get_current_stream() == self.stream
      with s1:
          assert cuda.get_current_stream() == s1
          s2.use()
          assert cuda.get_current_stream() == s2
          with s3:
              assert cuda.get_current_stream() == s3
              del s2
          assert cuda.get_current_stream() == s1
      # self.stream is "forgotten"!
      assert cuda.get_current_stream() == cuda.Stream.null
  
imports: import gc
  import threading
  import unittest
  import pytest
  import cupy
  from cupy._creation import from_data
  from cupy import cuda
  from cupy import testing
label_desc: Use image node_id 15 for calling the TestStream obj's underlying member method code with example usage: obj.test_mix_use_context() without return types