Adding an optional validation stage, that if it exists will be run be…

…fore the main part of a stage

ceci/stage.py

@@ -148,6 +148,10 @@ def get_aliased_tag(self, tag):
     def run(self):  # pragma: no cover
         """Run the stage and return the execution status"""
         raise NotImplementedError("run")
+
+    def validate(self):
+        """Check that the inputs actually have the data needed for execution"""
+        pass 
 
     def load_configs(self, args):
         """
@@ -661,6 +665,16 @@ def execute(cls, args, comm=None):
         if args.memmon:  # pragma: no cover
             monitor = MemoryMonitor.start_in_thread(interval=args.memmon)
 
+        # Now we try to see if the validation step has been changed,
+        # if it has then we will run the validation step, and raise any errors
+        try:
+            stage.validate()
+        except Exception as error:
+            print(f"Looks like there is an validation error in: {cls.name}")
+            print(error)
+            raise
+
+
         try:
             stage.run()
         except Exception as error:  # pragma: no cover