Inject steps at runtime about cucumber-js

[davidjgoss]

Injecting fresh steps dynamically at runtime isn't something we'll be doing, it would be a big departure from the current model of Cucumber.

The other way to resolve this is just to do the assertion in the step. However, we've decided that having the step do the request and the assertion is mixing concerns, only "Outcome" steps should be making assertions.

I see where you're coming from here, and it's good to avoid mixing concerns, but it's generally an accepted practise to do assertions like this on context steps. They're in a different category to assertions that validate functional outcomes, because they're just about ensuring the state is as expected.