What’s wrong with the V model?

I will use the V model as an example of a bad model. I use it because it’s the most familiar.


A typical version of the V model begins by describing software development as
following the stages shown here:

That’s the age-old waterfall model. As a development model, it has a lot of problems. Those don’t concern us here – although it is indicative of the state of testing models that a development model so widely disparaged is the basis for our most common testing model. My criticisms also apply to testing models that are embellishments on better development models, such as the spiral model.

Testing activities are added to the model as follows:

Unit testing checks whether code meets the detailed design. Integration testing checks whether previously tested components fit together. System testing checks if the fully integrated product meets the specification. And acceptance testing checks whether the product meets the final user requirements.


To be fair, users of the V model will often separate test design from test implementation. The test design is done when the appropriate development document is ready.

This model, with its appealing symmetry, has led many people astray.