Declarative approach to define requirements

[ivergara]

The current approach of defining constraints against a datasource is fairly 'imperative'. It has been suggested that a more natural approach would lean towards a more 'declarative' approach.

In light of limiting complexity around data tests as much as possible, one could look at a specification as more of a 'configuration' - merely expressing expectations in a simple fashion and not relying on mutations, control flow and loops.

It could be possible to provide an additional API to express constraints: at creation time of a Requirement object. A user could then voluntarily opt in to look at Requirement objects in an immutable fashion. This could but wouldn't need to happen in a wrapper around Requirement.

For now, we are not sure about how to evaluate the upside of such an alternative, more high-level API. Hence, we decided to stay alert and let the idea sink in without a concrete next step.

cc @jonashaag @kklein