BDD Are scenarios exclusive?

Question

If two scenarios can occur at the same time, does that (always/ever) constitute a third scenario?

My current thinking is that they are not necessarily exclusive (depends on the scenario). If you have two scenarios that could occur at the same time that they would only require a third scenario if the Given/When/Then steps do not merge implicitly or if one scenario takes precedence over the other.

This question has arisen whilst thinking about scenarios for what is essentially a form of injection in which Collections of objects get injected into another object ( https://github.com/jameskennard/mockito-collections ). So given the two scenarios "Class of object under test has a List of collaborators" and "Class of object under test has a Set of collaborators". Both could occur at the same time so a third scenario could be "Class of object under test has a List and a Set of collaborators". But it doesn't feel right, it's just too verbose, I think the Given/When/Then steps would be seen to merge implicitly. (Have a bad feeling I may have just answered my own question)

Anyone have any differing thoughts?

Answer 1

I think the key here is the behavior. The potential third scenario ("Class of object under test has a List and a Set of collaborators") that you're asking about is of course real but the behavior is already covered by the other two scenarios so I'd say there is no need to write another scenario.

If the combination of givens was to result in different behavior there would certainly be a third scenario but I believe the two you have cover the behavior you're looking to define.

Answer 2

At the moment, your sentences above are describing state rather than behavior.

What is the different outcome you get in each of the different contexts? I would expect something like this:

Given my CUT has five collaborators
When I do my thing with the class
Then it should use each collaborator in turn.

Given my CUT has five collaborators
And the fourth and fifth collaborators are identical
When I do my thing with the class
Then it should only use the fourth collaborator once.

That would illustrate the different behavior of the list (ordered) and the set (no duplicates).

If those two elements are truly beneficial independently, then yes, they're two separate scenarios. If they both have to be present for the class to have any value, I'd merge them into one:

Given my CUT has five collaborators
And the fourth and fifth collaborators are identical
When I do my thing with the class
Then it should use each collaborator in turn
And it should only use the fourth collaborator once.

An example of two simultaneous benefits might be getting cash out of an ATM, in which the cash is delivered and the account is also debited. You couldn't do either of those independently. Offering a receipt for the transaction would be a separate benefit, as it doesn't need to occur for an ATM to be of value. Hope this helps to make the distinction.