input: Write a python function to split a dataset into training and testing sets using sklearn's train_test_split method.
  assert len(train_test_split([1, 2, 3, 4, 5], [0, 1, 0, 1, 0], test_size=0.4, random_state=42))==4
  assert len(train_test_split([[1, 2], [3, 4], [5, 6], [7, 8]], [0, 1, 0, 1], test_size=0.25, random_state=42))==4
output: from sklearn.model_selection import train_test_split
  
  def split_dataset(X, y, test_size=0.2, random_state=None):
      return train_test_split(X, y, test_size=test_size, random_state=random_state)