In older development models (like waterfall), development activities were centered around the idea of a hand off—when one team completed its tasks, it handed the software off to the next team, keeping responsibilities and activities siloed. The justification for these separate steps was an emphasis on quality. Teams had more time to perform their specific tasks and guarantee the best result.
With demand for increased development speeds, however, this older model was no longer viable. Organizations needed a means of developing and delivering to their customers faster. A newer development model, agile, evolved to address this ever-increasing demand for development velocity. In this model, organizations introduced more incremental activities, performed continuously.
Currently, most organizations have adopted DevOps and DevSecOps, which uses an environment of collaboration and shared responsibility. This shift away from older practices has enabled teams to embrace automation and continuous activities. Continuous testing is one of these key practices.