Check there are scenarios

1 files changed, 6 insertions, 0 deletions

diff --git a/yarn b/yarn
index 3e9be0d..a84fcd4 100755
--- a/yarn
+++ b/yarn
@@ -109,6 +109,7 @@ class YarnRunner(cliapp.Application):
                 'step %Index(step,steps): %String(step_name)')
 
         scenarios, implementations = self.parse_scenarios(args)
+        self.check_there_are_scenarios(scenarios)
         self.check_for_duplicate_scenario_names(scenarios)
         self.check_for_thens(scenarios)
         self.connect_implementations(scenarios, implementations)
@@ -160,6 +161,11 @@ class YarnRunner(cliapp.Application):
 
         return block_parser.scenarios, block_parser.implementations
 
+    def check_there_are_scenarios(self, scenarios):
+        if not scenarios:
+            raise cliapp.AppException(
+                'There are no scenarios; must have at least one.')
+
     def check_for_duplicate_scenario_names(self, scenarios):
         counts = collections.Counter()
         for s in scenarios: