Use Cases and Testing

In today's testing world there is good news and bad news. The good news is that, more and more, testers are being asked to evaluate the quality of object-oriented analysis and design work earlier in the development process. The bad news is that most of us do not have an extensive background in the object-oriented paradigm or in UML (Unified Modeling Language), the notation used to  ocument object-oriented systems.

This is the first in a series four of articles written to

• introduce you to the most important diagrams used in object-oriented development (use case diagrams, sequence diagrams, class diagrams, and state-transition diagrams)
• describe the UML notation used for these diagrams
• give you as a tester a set of practical questions you can ask to evaluate the quality of these object-oriented diagrams

We will use three independent approaches to test our diagrams:

• syntax
  "Does the diagram follow the rules?"
• domain expert
  "Is the diagram correct?" "What else is there that is not described in this diagram?"
• traceability
  "Does everything in this diagram trace back correctly and completely to its predecessor?" "Is everything in the predecessor reflected completely and correctly in this diagram?"

For this set of articles we will use a case study: a Web-based, online auction system that I invented: F-LAKE. Yes, I invented the idea of online auctions. I'm not sure why F-LAKE never caught on.

Use Cases
A use case is a scenario that describes the use of a system by an actor to accomplish a specific goal. What does this mean? An actor is a user playing a role with respect to the system. Actors are generally people although other computer systems may be actors. A scenario is a sequence of steps that describe the interactions between an actor and the system. The use case model consists of the collection of all actors and all use cases. Use cases help us

• capture the system's functional requirements from the users' perspective
• actively involve users in the requirements-gathering process
• provide the basis for identifying major classes and their relationships
• serve as the foundation for developing system test cases

The UML notation for use cases is

 
The rectangle represents the system boundary, the stick figures represent the actors (users of the system), and the ovals represent the individual use cases. Unfortunately, this notation tells us very little about the actual functionality of the system.

Alistair Cockburn has proposed the following format for defining the details of each use case, which I have used on a number of projects. I've included an example use case for F-LAKE: "Bid On An Item."

Syntax Testing
Let's begin with the simplest kind of testing-syntax testing. When performing syntax testing,