code: def test_incorrect_data(self):
      self.assertRaises(ValueError, ema, [], 2)
  
imports: import unittest
  import matplotlib
  from pyclustering.cluster.ema import ema, ema_observer, ema_initializer, ema_init_type, ema_visualizer
  from pyclustering.utils import read_sample
  from pyclustering.samples.definitions import SIMPLE_SAMPLES, FCPS_SAMPLES, FAMOUS_SAMPLES
label_desc: Use image node_id 31 for calling the EmaUnitTest obj's underlying member method code with example usage: obj.test_incorrect_data() without return types