Hypothetical BDD syntaxt for bigtest that uses generators to build a test tree

describe.ts

import { Page, TextField, Button, HTML, Heading, including } from '@bigtest/interactor';
import { describe } from '@bigtest/suite/bdd'; //hypothetical bdd syntax entry point
import { createUser } from './helpers';

export default describe("login test", function*() {
  yield createUser("cowboyd", "password"); //=> injects `user` into context
  yield Page.visit('/sign-in');
  yield Heading(including('Sign into app')).exists();

  yield describe("with good credentials", function*() {
    yield ({ user }) => TextField("username").fillIn(user.username);
    yield ({ user }) => TextField("password").fillIn(user.password);
    yield Button("Sign in").click();
  });

  yield describe("with bad credentials", function*() {
    yield TextField("username").fillIn("nobody");
    yield TextField("password").fillIn("not-gonna-happen");

    yield Button("SignIn").click();

    yield HTML({ id: 'sigin-errors'}).has({ text: including('password does not match') })
  })

})