Software Testing

May 12th, 2009

WaterFall Model is the most common and classic of life cycle models, also referred to as a linear-sequential life cycle model. WaterFall Model is very simple to understand and use.  In a waterfall model, each phase must be completed in its entirety before the next phase can begin.  At the end of each phase, a review takes place to determine if the project is on the right path and whether or not to continue or discard the project.  Unlike what I mentioned in the general model, phases do not overlap in a waterfall model.

Requirements: Defines needed information, function, behavior, performance and interfaces.

Design: Data Structures, software architecture, interface representations, algorithmic details.

Implementation: Source code, database, user documentation, testing.

Advantages:

• Simple and easy to use.
• Easy to manage due to the rigidity of the model – each phase has specific deliverables and a review process.
• Phases are processed and completed one at a time.

Works well for smaller projects where requirements are very well understood.

Disadvantages:

• Adjusting scope during the life cycle can kill a project
• No working software is produced until late during the life cycle.
• High amounts of risk and uncertainty.
• Poor model for complex and object-oriented projects.
• Poor model for long and ongoing projects.
• Poor model where requirements are at a moderate to high risk of changing.

When to Use Water Fall Model:

• Requirements are very well known.
• Product definition is stable.
• Technology is understood.
• New version of an existing product.
• Porting an existing product to a new platform.

SDLC:Software Development Lifecycle Model

Requirements

Business requirements are gathered in this phase.  Who is going to use the system?  How will they use the system?  What data should be input into the system?  What data should be output by the system?  These are general questions that get answered during a requirements gathering phase. This phase is the main focus of the project managers and stake holders.  Meetings with managers, stake holders and users are held in order to determine the requirements.  This produces a nice big list of functionality that the system should provide, which describes functions the system should perform, business logic that processes data, what data is stored and used by the system, and how the user interface should work.  The overall result is the system as a whole and how it performs, not how it is actually going to do it.

Design

The software system design is produced from the results of the requirements phase.  Architects have the ball in their court during this phase and this is the phase in which their focus lies.  This is where the details on how the system will work is produced.  Architecture, including hardware and software, communication, software design (UML is produced here) are all part of the deliverables of a design phase.

Implementation

Code is produced from the deliverables of the design phase during implementation, and this is the longest phase of the software development life cycle.  For a developer, this is the main focus of the life cycle because this is where the code is produced.  Implementation my overlap with both the design and testing phases.  Many tools exists (CASE tools) to actually automate the production of code using information gathered and produced during the design phase.

Testing

During testing, the implementation is tested against the requirements to make sure that the product is actually solving the needs addressed and gathered during the requirements phase.  Unit tests and system/acceptance tests are done during this phase.  Unit tests act on a specific component of the system, while system tests act on the system as a whole.

So in a nutshell, that is a very basic overview of the general software development life cycle model.  Now lets delve into some of the traditional and widely used variations.