Scenario

A scenario is a boolean assertion. Given / When / Then — pass or fail. It answers one question: given this exact situation, does it do that — yes or no?

It is fine-grained and testable. Where a use case describes an actor, their goal, the way in, and everything else that can happen, a scenario proves one observable behavior — and it is drawn from the capability’s control-flow graph, not from the use-case prose.

What a scenario looks like

Scenarios live in the .feature file as pure boolean Gherkin:

Scenario: the Scanner fires when a spec ships
  Given a spec transitions to implemented
  When the Scanner observes the terminal transition
  Then it drafts strategy from the finished mission

The rules that keep a scenario boolean:

• Every Then is a boolean assertion of observable behavior — the subject does X, not does X sometimes. No probabilities, no “usually.”
• Observable behavior only — assert outputs, exit codes, side effects, emitted events. Never internal state, function names, or implementation steps.
• No rubric in the scenario — threshold and score are the judge’s private detail. A non-deterministic subject still collapses to one boolean (score ≥ threshold → pass/fail).

Where scenarios live

Scenarios live in the .feature, never in spec.md. They trace the workflow top-to-bottom, grouped by stage, so a reader can audit that every stage is covered.

Scenario vs use case

A scenario is fine and lives in the .feature; a use case is coarse and lives in spec.md. The relationship is one-to-many: one use case is verified by one or more scenarios, and it is never one-to-one — one of a use case’s extensions may need several scenarios where several paths reach it, and several extensions may converge on one.

Scenarios come from the control-flow graph, never from the use-case prose. That direction is load-bearing: a suite derived from a written list is complete against that list by construction, so it can no longer surface a gap. A scenario with no use case is an orphan test — it asserts a behavior nobody entered through.