fix iteration, add test

src/main/scala/de/tum/workflows/toz3/InvariantChecker.scala

@@ -103,6 +103,7 @@ object InvariantChecker extends LazyLogging {
       // check if done, i.e. all edges proven
       val toProve = (graph.edges -- proven)
       if (toProve.isEmpty) {
+        logger.info("Everything proven. Terminating.")
         Some(labels)
       } else {
 
@@ -116,7 +117,8 @@ object InvariantChecker extends LazyLogging {
 
         if (status == Status.UNSATISFIABLE) {
           // Negation of implication unsat
-          // --> safe, continue with larger proven set
+          // --> safe, continue with larger proven set.
+          logger.info(s"Proven inductiveness for (${next._1} -> ${next._2}).")
           checkInvariantRec(labels, proven + next)
         } else {
           // Negation of implication sat
@@ -132,6 +134,7 @@ object InvariantChecker extends LazyLogging {
             // Negation of newinv still unsat, newinv still sat
             checkInvariantRec(newlabels, newproven)
           } else {
+            logger.info("New invariant not satisfiable. Terminating.")
             None
           }
         }