Represents what should be the case about some part of the world.

Expectations are checked at the end of the scenario, after all steps of the script have been performed.

An Observer determines whether to accept or reject a claim with respect to some particular part of the world. It is a function from a claim to an Expectation that will be evaluted at the end of the scenario.

Observe some aspect of the model of the program whose behavior is being described in this scenario.

For example, if the program model looks like { score: 27 }, then you could observe the score like so:

Spec.it "has the correct score" (
  observeModel .score
    |> Spec.expect 
      (Spec.Claim.isEqual Debug.toString 27)
)

Check out Spec.Markup, Spec.Http, Spec.Port, and Spec.Witness for observers that evaluate claims with respect to the world outside the program.

Create a new Observer that will evaluate a Claim with respect to the successful Result observed by the given Observer. If the Result fails then the Claim will be rejected.

Create a new Observer that will map the Report created if the Claim is rejected.