We define test data as any data we consistently use to verify a certain property, like functionality or performance, of a system. Another popular term for the same concept is fixture. We will use these interchangeably.
Headless browsers can be leveraged for testing in a variety of ways, and different scenarios do command different approaches. That being said, there are some general pointers most should follow in order to keep their tests valuable.
Here, we define valuable as sustainably expressing meaningful, truthful information about the state of a system. A test that does not reliably fulfill these criteria should be fixed, if possible, or simply removed.