I’m quite surprised by this response. I find the Folio pitch very compelling, I’m a TypeScript fanatic, and the TS accommodations are pretty low down the list f

I’m quite surprised by this response. I find the Folio pitch very compelling, I’m a TypeScript fanatic, and the TS accommodations are pretty low down the list for me in this case. For me the isolation story is by far the most interesting. Of course you can wrap an existing test framework to provide different kinds of isolation, to some extent. There are some things you can’t do with most if not all of the BDD-style JS test frameworks I can recall, for instance any kind of `aroundEach` where a test’s setup, execution and teardown can run in a shared call stack. This is useful (for instance) in situations where you might use CLS to wrap a test in a database transaction. At least walking up to this, that appears to be solved by their interface. Another thing it solves is providing matrix testing primitives where you can branch at the framework level depending on arbitrary environment differences. This is a godsend for library authors, and also for anyone integrating with a variety of external dependencies. Again, of course that could be solved by wrapping some more naive framework. But having the primitives first class and built in means: - You’re not reinventing the wheel. - There’s an idiomatic way to do it. That’s huge! This is stuff I’ve one-offed a zillion times because it never felt quite right. Now it’s a potentially shared problem, and people can coalesce around the solution.