code: def testNonExistentFilesystem(self):
      with self.assertRaises(ValueError):
          gfile.get_filesystem("nonexistent::blah://filesystem")
  
imports: import posixpath
  from tensorboard import test
  from tensorboard.compat.tensorflow_stub import errors
  from tensorboard.compat.tensorflow_stub.io import gfile
  import fsspec
label_desc: Use image node_id 21 for calling the GFileFSSpecTest obj's underlying member method code with example usage: obj.testNonExistentFilesystem() without return types