> What does it mean to the marketplace?

It's not supposed to inherently mean something, it's just supposed to be unique. The descriptive text is intended to be consumed by humans, not this.

> Why not in the scenario? That would make it easier for the engineer implementing the scenarios.

Because that would be redundant. The 'conforms with the schema' already does this check.

I actually really dislike asserting on these long-form messages because these tests are generally brittle.