code: def _check_png(self, data):
      # If it has a valid PNG header, we can assume it did the right thing.
      # We trust the underlying `encode_png` op.
      self.assertEqual(b"\x89PNG", data[:4])
  
file_path: tensorboard/tensorboard/util/encoder_test.py
imports: import numpy
  import tensorflow
  from tensorboard.util import encoder
label_desc: Use image node_id 2 for calling the TensorFlowPngEncoderTest obj's underlying member method code with example usage: obj._check_png(data) without return types