Models for Testing

Waterfall Model

The waterfall model is also known as the sequential model. It is where the development stage occurs sequentially one after another followed by testing in block at the end after the code has been delivered.

Unfortunately it is still widely used today due to the misconception that testing starts with the delivery of the code.

Problems of the waterfall model

· Testing starts with delivery of code and so testers tends to base their judgement on the behaviour of code rather than the documents.

· Errors are more costly to correct due to testing starting later in the SDLC.

· Testing phase is sometimes or always reduced when the project is over budget or exceeding timescales.

Testing is done as test execution only.

The V-Model

The V-Model is a model designed in a way that testing starts from the inception of the project. For every corresponding phase of the SDLC there is an equal phase of testing.

Advantages of the V-Model

· Testing is based on documentation and not the code.

· Correct test are created.

· Errors are found early within the SDLC.

· Cost of failure is less expensive.

· There is an in built quality.

By adhering to the V Model testers are more likely to create the correct test as they are using the requirements and system specification to derive test conditions rather than code as it was previously done. Testing is now seen as an activity to be performed throughout the SDLC rather than just a phase at the end of the SDLC.

By introducing these activities, or quality control points, we are more likely to create systems that are fit for purpose.

Spiral Model

This differs significantly from the previous models. It is the incremental approach to development and testing whereby the full system requirements may not be known at the start of the project.

The initial requirements will be defined, designed built and tested and anytime there is an enhancement or change of the requirements, there will be another definition, design, build and testing to the system.

Rapid Application Development (RAD)

This is a model where the system can be developed and implemented quickly. Here the system requirements are understood at the beginning of the project, however these requirements are not formally documented, but split down into components or functions which are each defined, developed, built and tested in parallel with a set of time allocated for testing. At the end of the time the components are then assembled together into a working version of the application. Documentation is always scarce or non-existent.

Dynamic Systems Development Methodology (DSDM)

This was put I place to put controls around the RAD. It is similar to RAD but just insists on the production and retention of documentation relating to the SDLC.

Verification Validation and Testing (VVT)

VVT can be thought as a good testing practice and can be applied to the earlier models.

Verification – is the confirmation by examination and provision of objective evidence that a specified requirement have been fulfilled.

Validation – is the confirmation by examination and provision of objective evidence that the particular requirements for a specific intended use have been fulfilled.

Testing – is a process of exercising that a software meets a specific requirement and to detect errors.

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