Example:

        ```py
        >>> from datasets import load_dataset
        >>> ds = load_dataset("rotten_tomatoes", split="validation")
        >>> ds = ds.train_test_split(test_size=0.2, shuffle=True)
        DatasetDict({
            train: Dataset({
                features: ['text', 'label'],
                num_rows: 852
            })
            test: Dataset({
                features: ['text', 'label'],
                num_rows: 214
            })
        })

        # set a seed
        >>> ds = ds.train_test_split(test_size=0.2, seed=42)