Testing python function

Hi everyone I'm beginner in python and I want to test my function.But I got errors.

 def picture(name, ext='.jpg'):
if name:
    return '.%s%s' % (name, ext)
else:
    return '%s' % (ext)
@pytest.mark.parametrize('input, expected_result',
                    [('first.jpg', True),
                    ('second', False)])    
def test_picture(input, expected_result):
assert picture(input)  == expected_result