Add default to mock_input() if no input, hide functions

tud_test_base.py

import builtins

input_values = []
print_values = []


def get_display_output():
    '''Get the printed output in list from the test target'''
    global print_values
    return print_values


def set_keyboard_input(mocked_inputs):
    """Set the input in list for 'input()'
    ['first input for the code', 'second text', ...]"""
    global input_values

    def mock_input_output_start():
        def mock_input(s=None):
            if s is not None:
                print_values.append(s)
            return input_values.pop(0)

        global input_values, print_values

        input_values = []
        print_values = []

        builtins.input = mock_input
        builtins.print = lambda s: print_values.append(s)

    mock_input_output_start()
    input_values = mocked_inputs