Article III, -2 II, contains perhaps the most important limitation of the judicial power: the “case” or “controversy” requirement. This limitation has spawned multiple restrictions on the scope of judicial authority including the prohibition against advisory opinions, the ripeness  and mootness doctrines, and the standing requirement.
A case is defined as a suit instituted according to the regular course of judicial procedures.
Marbury v. Madison
For a controversy to exist, the parties must have adverse interests. Muskrat v. United States.
There must be an “honest and actual antagonistic assertion of rights.  Chicago & G.T.Ry. Co. v. Wellman.