What he wrote is basically "don't repeat in test X what you already tested in test X-1".

It's not as much composition as compounding, and can work quite well.

Let's say something takes 20 steps, and you want to test all 20.

Instead of this:

    test 1:
       do step 1, assert step 1

    test 2:
       do step 1, assert step 1
       do step 2, assert step 2

    test 3:
       do step 1, assert step 1
       do step 2, assert step 2
       do step 3, assert step 3

    ...

you do this:

    test 1:
       do step 1, assert step 1

    test 2:
       do step 1
       do step 2, assert step 2

    test 3:
       do step 1
       do step 2
       do step 3, assert step 3

    ...

This works well in certain situations, as it skips diplicated redundant testing. Requires some discipline so that tests don't drift away from each other.

As most things, it depends on what those steps are. Perhaps you only need that one final (integration) test instead of 20 intermediate unit ones.