Alternative simple syntax for unit_test to be used as a with context

[acbart]

Writing up the SIGCSE slides, I realized that unit_test is a bit ugly in its current form. It's also a lot less flexible than it could be.

unit_test('cube_elements',
            ([[1, 2, 3]], [1, 8, 27]),
            ([[1]], [1]),
            ([[4, 4, 4]], [64, 64, 64]),
            ([[0]], [0]),
            ([[]], []))

I've dealt with it for years on my own, but for other people, I think the following syntax would be nice:

with unit_test('cube_elements'):
    assert_equal(cube_elements([1, 2, 3]), [1, 8, 27])
    assert_equal(cube_elements([1]), [1])
    assert_equal(cube_elements([4, 4, 4]), [64, 64, 64])
    assert_equal(cube_elements([0]), [0])
    assert_equal(cube_elements([]), [])

I've got the basics of the context version down; if you call unit_test without any tests, then it just returns the with context manager object. The only part that needs additional work is handling the each_score[test_index] logic.