text: from nbconvert.filters import get_metadata
  
  def test_get_metadata():
      output = {
          'metadata': {
              'width': 1,
              'height': 2,
              'image/png': {
                  'unconfined': True,
                  'height': 3,
              }
          }
      }
      assert get_metadata(output, 'nowhere') is None
      assert get_metadata(output, 'height') == 2
      assert get_metadata(output, 'unconfined') == None
      assert get_metadata(output, 'unconfined', 'image/png') == True
      assert get_metadata(output, 'width', 'image/png') == 1
      assert get_metadata(output, 'height', 'image/png') == 3
  