BDD Design Patterns: Reference Tracker

Writing BDD stories and implementing the steps you will soon come to the point to deal with references between steps, like:

Given I have a document A on disk
When I open document A
And I change the content of document A
And I save document A
Then document A on disk will be updated
And document A will contain the new content

Reading this you will find two references to be tracked:

• the document itself
• the content which got changed

I found many implemented solutions for this pattern, each of them a little different. Some using global variables and a central class to hold all steps, others using singletons.

Summarizing the solutions I found I introduced a new pattern which got quite positive feedback: the Reference Tracker.

The basic idea is that you will have three items to track:

1. the type of the reference (here: document or content)
2. the reference name (here: A once, unnamed the other)
3. the actual reference value

Having this you just need two methods to feed the tracker and to retrieve values from it:

The cleanup() method should ensure that you don’t collide with new scenarios. In JBehave context you should call it in @AfterScenario.

For the example above you would implement the interface with:

• Key-Type: String (“document”, “content”)
• Value-Type: Object (once file, once String, XML or whatever)

The complete Gist contains another implementation called TypedReferenceTracker which assumes that the value-type is the same as the key, so that there is a class for documents and one for contents. It makes the getter a little easier to use.

Find the complete Gist at GitHub.