These sorts of tests are invaluable for things like ensuring adherence to specifications such as OAuth2 flows. A high-level test that literally describes each step of a flow will swiftly catch odd changes in behavior such as a request firing twice in a row or a well-defined payload becoming malformed. Say a token validator starts misbehaving and causes a refresh to occur with each request (thus introducing latency and making the IdP angry). That change in behavior would be invisible to users, but a test that verified each step in an expected order would catch it right away, and should require little maintenance unless the spec itself changes.