Which model of software development emphasizes continuous testing throughout the lifecycle?

The V-Model, or Verification and Validation model, emphasizes continuous testing throughout the software development lifecycle by integrating testing activities directly with each corresponding development phase. In this model, development and testing are structured in a way that each development phase has a related testing phase, creating a 'V' shape when visualized.

As developers design and implement parts of the software, testing occurs concurrently, ensuring that any issues are identified and addressed immediately rather than at the end of the development process. This approach allows for a more robust verification of requirements against the actual implementation, enhances quality assurance, and ultimately leads to a more reliable product.

In contrast, other models like the Waterfall model follow a more linear progression where testing happens only after the completion of the development phase. The Agile model does focus on iterative processes and adaptive planning but does not emphasize the structured relationship between development and testing in the same definitive manner as the V-Model. The Spiral model combines elements of design and prototyping in stages but does not specifically highlight constant testing through all phases as integrally as the V-Model does.