input: Write a python function to add two matrices and return the result.
  assert np.array_equal(add(np.array([[1, 2], [3, 4]]), np.array([[5, 6], [7, 8]])), np.array([[6, 8], [10, 12]]))
  assert np.array_equal(add(np.array([[1, 2, 3], [4, 5, 6]]), np.array([[7, 8, 9], [10, 11, 12]])), np.array([[8, 10, 12], [14, 16, 18]]))
  assert np.array_equal(add(np.array([[1]]), np.array([[2]])), np.array([[3]]))
output: def add(matrix1, matrix2):
      return np.add(matrix1, matrix2)