Ability to write tests in Javascript

The ability to write TDD-style tests using Javascript to be executed after a request is sent. It would be nice to follow the existing pattern, and make sure that the API is compatible with Postman. This makes it easier for new users to switch to Testfully from Postman.

Examples:

test("should return 200 OK", () => {
   expect($.response.code).to.equal(200);
});