docstr: %%px --[no]block flags work
code: def test_cellpx_block_args(self):
      """%%px --[no]block flags work"""
      ip = get_ipython()
      v = self.client[-1:]
      v.activate()
      v.block = False
  
      for block in (True, False):
          v.block = block
          ip.run_line_magic("pxconfig", "--verbose")
          with capture_output(display=False) as io:
              ip.run_cell_magic("px", "", "1")
          if block:
              assert io.stdout.startswith("Parallel"), io.stdout
          else:
              assert io.stdout.startswith("Async"), io.stdout
  
          with capture_output(display=False) as io:
              ip.run_cell_magic("px", "--block", "1")
          assert io.stdout.startswith("Parallel"), io.stdout
  
          with capture_output(display=False) as io:
              ip.run_cell_magic("px", "--noblock", "1")
          assert io.stdout.startswith("Async"), io.stdout
  
imports: import re
  import signal
  import sys
  import time
  import pytest
  from IPython import get_ipython
  from IPython.utils.io import capture_output
  import ipyparallel
  from ipyparallel import AsyncResult
  from .clienttest import ClusterTestCase, generate_output, raises_remote
label_desc: Use image node_id 6 for calling the TestParallelMagics obj's underlying member method code with example usage: obj.test_cellpx_block_args() without return types