So for tests, we've tried to follow along with a somewhat Jasmine-like "X should Y" description structure, though I'm not sure how consistent we've been. The top-level groups are classes. Any nested groups might be methods, if the class is complex, and tests are specific behaviors being tested. The descriptions are concatenated by the runner, so it's nice to read a sentence like "TreeSet when empty should have no elements", etc.

It can be more cumbersome, but it'd be like this:

```
group("TreeSet", () {
  group("when empty", () {
    var tree;
    setUp(() { new TreeSet<num>(); });
    test("should actually be empty", () { expect(tree, isEmpty); });
    test("should not contain an element", () { expect(tree.lookup(0), isNull); });
  });
});
```

or something... because there are cross-cutting concerns that don't fit a hierarchy nicely, like "when empty", "when added to" and lookup, length, nearest, etc. I still don't have an ideal organization down, but I lean towards grouping by method as much as possible.

So for now, how about expanding on a few of the descriptions. Like "(perf)"? We can try to unify testing styles later.