Add support for worlds

Cucumber runs scenarios in a world, and different worlds can be created that execute the steps differently, depending on the world. For example, a Web UI world could execute a step by interacting with a web page in a browser (i.e. navigating, entering input, clicking buttons/links, etc); an iOS or Android world could execute the same steps in a native iOS or Android app; an API world could execute the exact same steps simply by calling API endpoints with no interaction with a UI at all; etc. This feature is incredibly useful from a maintenance perspective, since it allows you to have a single place to define all of your step definitions using a ubiquitous language, while at the same time being able to define the actual execution of each step in a separate world file/object.

See the Cucumber wiki for more information on this feature.

Start with the linked Cucumber wiki page, “A Whole New World,” to understand the proposed world model and compare it with pytest-bdd’s current behavior. Identify the project entry points and tests that would need to define and execute worlds; done means the intended world-specific step execution is supported and covered by tests.