input: Write a python function to split data into training and testing sets.
  assert len(train_test_split(np.array([[1, 2], [3, 4], [5, 6], [7, 8]]), [0, 1, 0, 1], test_size=0.5, random_state=0)) == 4
  assert len(train_test_split(np.array([[1, 2], [3, 4], [5, 6], [7, 8], [9, 10]]), [0, 1, 0, 1, 0], test_size=0.4, random_state=42)) == 4
output: import numpy as np
  from sklearn.model_selection import train_test_split as sk_train_test_split
  
  def train_test_split(X, y, test_size=0.25, random_state=None):
      X_train, X_test, y_train, y_test = sk_train_test_split(X, y, test_size=test_size, random_state=random_state)
      return X_train, X_test, y_train, y_test