docstr: ...Test HawkesKernelSumExp decay
          
code: def test_HawkesKernelSumExp_n_decays(self):
      """...Test HawkesKernelSumExp decay"""
      self.assertEqual(
          self.hawkes_kernel_sumexp.n_decays, len(self.decays)
      )
  
file_path: tick/tick/hawkes/simulation/tests/hawkes_kernel_sum_exp_test.py
imports: import unittest
  import numpy
  from tick.hawkes import HawkesKernelSumExp
label_desc: Use image node_id 4 for calling the Test obj's underlying member method code with example usage: obj.test_HawkesKernelSumExp_n_decays() without return types