--- order a_, b_ (alphabetical) ---
a_registersUser() -> SUCCESSFUL
b_assumesUserExists() -> SUCCESSFUL
--- order b_, a_ (reversed) ---
b_assumesUserExists() -> FAILED
a_registersUser() -> SUCCESSFUL
  AssertionFailedError: registry should contain the user registered by another test ==> expected: <1> but was: <0>
--- time: the same code with an injected Clock ---
acceptsOrders() at 10:00 UTC : true
acceptsOrders() at 23:30 UTC : false