Implement check for duplicate scenario names

2 files changed, 16 insertions, 0 deletions

diff --git a/yarn b/yarn
index 3bb26e8..c13681b 100755
--- a/yarn
+++ b/yarn
@@ -18,6 +18,7 @@
 
 
 import cliapp
+import collections
 import logging
 import os
 import re
@@ -108,6 +109,7 @@ class YarnRunner(cliapp.Application):
                 'step %Index(step,steps): %String(step_name)')
 
         scenarios, implementations = self.parse_scenarios(args)
+        self.check_for_duplicate_scenario_names(scenarios)
         self.check_for_thens(scenarios)
         self.connect_implementations(scenarios, implementations)
         shell_prelude = self.load_shell_libraries()
@@ -158,6 +160,17 @@ class YarnRunner(cliapp.Application):
 
         return block_parser.scenarios, block_parser.implementations
 
+    def check_for_duplicate_scenario_names(self, scenarios):
+        counts = collections.Counter()
+        for s in scenarios:
+            counts[s.name] += 1
+
+        duplicates = [name for name in counts if counts[name] > 1]
+        if duplicates:
+            duplist = ''.join('  %s\n' % name for name in duplicates)
+            raise cliapp.AppException(
+                'There are scenarios with duplicate names:\n%s' % duplist)
+
     def check_for_thens(self, scenarios):
         no_thens = []
         for scenario in scenarios:
diff --git a/yarn.tests/duplicate-scenario-names.stderr b/yarn.tests/duplicate-scenario-names.stderr
new file mode 100644
index 0000000..d3fbc95
--- /dev/null
+++ b/yarn.tests/duplicate-scenario-names.stderr
@@ -0,0 +1,3 @@
+ERROR: There are scenarios with duplicate names:
+  foo
+