docstr: ...Test PoissonRegression loglik function
          
docstr_tok: ["...","Test","PoissonRegression","loglik","function"]
code: def test_loglik(self):
      """...Test PoissonRegression loglik function"""
      X_train, y_train, _, _ = self.get_train_data(
          n_samples=200, n_features=12
      )
      learner = PoissonRegression(random_state=32789, tol=1e-9)
      learner.fit(X_train, y_train)
      X_test, y_test, _, _ = self.get_train_data(
          n_samples=5, n_features=12
      )
      np.testing.assert_array_almost_equal(
          learner.loglik(X_test, y_test), 1.8254, decimal=4
      )
  
imports: import unittest
  from itertools import product
  import numpy
  from tick.base.inference import InferenceTest
  from tick.linear_model import SimuPoisReg, PoissonRegression
  from tick.simulation import weights_sparse_gauss
label_desc: Use image node_id 15 for calling the Test obj's underlying member method code with example usage: obj.test_loglik() without return types