Definition: Response time testing measures how long a system or feature takes to respond to a request or complete an action. In an agile context, it is often run on each newly developed feature as soon as it passes functional testing, and the results are compared against agreed performance acceptance criteria.
So what? Users notice slow responses before they notice most other performance problems. Testing response times feature by feature gives developers fast, specific feedback they can act on within the same sprint.
Examples: Measuring how long a search results page takes to load once the search story is signed off. Checking that a checkout step responds within the time agreed with the product owner.
