From 7cba7b30e615e627984047b00cdd0de0b201efb5 Mon Sep 17 00:00:00 2001
From: Lars Wirzenius <liw@liw.fi>
Date: Sun, 25 Aug 2013 13:54:49 +0100
Subject: Check there are scenarios

---
 NEWS                           | 3 +++
 yarn                           | 6 ++++++
 yarn.tests/no-scenarios.exit   | 1 +
 yarn.tests/no-scenarios.script | 9 +++++++++
 yarn.tests/no-scenarios.stderr | 1 +
 5 files changed, 20 insertions(+)
 create mode 100644 yarn.tests/no-scenarios.exit
 create mode 100755 yarn.tests/no-scenarios.script
 create mode 100644 yarn.tests/no-scenarios.stderr

diff --git a/NEWS b/NEWS
index 67d870f..a57a186 100644
--- a/NEWS
+++ b/NEWS
@@ -21,6 +21,9 @@ Bug fixes:
 * Yarn now complains if a scenario has no THEN steps. Suggested by
   Richard Maw.
 
+* Yarn now gives an error if there are no scenarios. Suggested by
+  Daniel Silverstone and others.
+
 * Yarn now checks for duplicate scenario names.
 
 Version 0.9, released 2013-07-23
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:
diff --git a/yarn.tests/no-scenarios.exit b/yarn.tests/no-scenarios.exit
new file mode 100644
index 0000000..d00491f
--- /dev/null
+++ b/yarn.tests/no-scenarios.exit
@@ -0,0 +1 @@
+1
diff --git a/yarn.tests/no-scenarios.script b/yarn.tests/no-scenarios.script
new file mode 100755
index 0000000..ffd8e96
--- /dev/null
+++ b/yarn.tests/no-scenarios.script
@@ -0,0 +1,9 @@
+#!/bin/sh
+
+set -eu
+
+
+cat <<EOF > "$DATADIR/test.yarn"
+EOF
+
+./run-yarn "$DATADIR/test.yarn"
diff --git a/yarn.tests/no-scenarios.stderr b/yarn.tests/no-scenarios.stderr
new file mode 100644
index 0000000..66311c1
--- /dev/null
+++ b/yarn.tests/no-scenarios.stderr
@@ -0,0 +1 @@
+ERROR: There are no scenarios; must have at least one.
-- 
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