docstr: ...Test plot_history rendering given a list of learners
          
code: def test_plot_history_learner(self):
      """...Test plot_history rendering given a list of learners"""
      learner1 = LogisticRegression(solver="svrg")
      learner1._solver_obj._set("history", self.solver1.history)
      learner2 = LogisticRegression(solver="agd")
      learner2._solver_obj._set("history", self.solver2.history)
  
      fig = plot_history([learner1, learner2], show=False)
      ax = fig.axes[0]
  
      ax_n_iter1, ax_obj1 = ax.lines[0].get_xydata().T
      np.testing.assert_array_equal(ax_n_iter1, self.n_iter1)
      np.testing.assert_array_equal(ax_obj1, self.obj1)
      self.assertEqual(ax.lines[0].get_label(), "SVRG")
  
      ax_n_iter2, ax_obj2 = ax.lines[1].get_xydata().T
      np.testing.assert_array_equal(ax_n_iter2, self.n_iter2)
      np.testing.assert_array_equal(ax_obj2, self.obj2)
      self.assertEqual(ax.lines[1].get_label(), "AGD")
  
file_path: tick/tick/plot/tests/plot_history_test.py
imports: import unittest
  import numpy
  from tick.linear_model import LogisticRegression
  from tick.plot import plot_history
  from tick.solver import GD, AGD, History
label_desc: Use image node_id 5 for calling the Test obj's underlying member method code with example usage: obj.test_plot_history_learner() without return types