In the following figure, we can see a roadmap to the BDD approach presented in this book:
A BDD roadmap
This figure is just a rough guide; just remember to use your common sense. Developing a test suite implies time and effort; if you do not expect to get enough value in return, just do not do it.
Of course, the architecture of your system may be different from the one I have presented; after all, I have just used one kind of architecture that is popular, but you might have a different one. However, you should always separate your domain layers from the technical ones and slice across functional domains.
Finally, here is a final summary of the whole book:
Always test the core layers where the domain logic resides. Use plain BDD and favor Cucumber whenever the stakeholders are willing to at least read it. See Chapter 3, Writing BDD Features and Chapter 4, Cucumber.js and Gherkin.
It is recommended that you test your web API layer using BDD as explained in Chapter 5, Testing...