From 0da0eb42be3ec77416d154336e36a2c6c19b1c6b Mon Sep 17 00:00:00 2001
From: Lars Wirzenius <liw@liw.fi>
Date: Tue, 21 Jan 2014 21:01:53 +0000
Subject: Add --allow-missing-steps

---
 NEWS |  4 ++++
 yarn | 22 ++++++++++++++++++++--
 2 files changed, 24 insertions(+), 2 deletions(-)

diff --git a/NEWS b/NEWS
index 555c610..5c99718 100644
--- a/NEWS
+++ b/NEWS
@@ -18,6 +18,10 @@ For yarn:
   but don't use the user's real home directory, which is important for
   test environment hygiene.
 
+* New option `--allow-missing-steps` to allow running a test suite
+  with some steps missing. The scenarios with missing steps will be
+  skipped. Suggested by Pete Fotheringham.
+
 For cmdtest:
 
 * The `--test` (`-t`) option should now work again. Thank you
diff --git a/yarn b/yarn
index ef19b94..af25d21 100755
--- a/yarn
+++ b/yarn
@@ -79,6 +79,11 @@ class YarnRunner(cliapp.Application):
             ['timings'],
             'report wall clock time for each scenario and step')
 
+        self.settings.boolean(
+            ['allow-missing-steps'],
+            'allow scenarios to reference steps that do not exist, '
+            'by warning about them, but otherwise ignoring the scenarios')
+
     def info(self, msg):
         if self.settings['verbose']:
             logging.info(msg)
@@ -117,7 +122,7 @@ class YarnRunner(cliapp.Application):
         self.check_there_are_scenarios(scenarios)
         self.check_for_duplicate_scenario_names(scenarios)
         self.check_for_thens(scenarios)
-        self.connect_implementations(scenarios, implementations)
+        scenarios = self.connect_implementations(scenarios, implementations)
         shell_prelude = self.load_shell_libraries()
 
         self.info('Found %d scenarios' % len(scenarios))
@@ -204,9 +209,17 @@ class YarnRunner(cliapp.Application):
                 ''.join('  "%s"\n' % s.name for s in no_thens))
 
     def connect_implementations(self, scenarios, implementations):
+        new_list = []
         for scenario in scenarios:
+            missing_step = False
             for step in scenario.steps:
-                self.connect_implementation(scenario, step, implementations)
+                self.connect_implementation(
+                    scenario, step, implementations)
+                if step.implementation is None:
+                    missing_step = True
+            if not missing_step:
+                new_list.append(scenario)
+        return new_list
 
     def connect_implementation(self, scenario, step, implementations):
         matching = [i for i in implementations
@@ -214,6 +227,11 @@ class YarnRunner(cliapp.Application):
                        self.implements_matches_step(i, step)]
 
         if len(matching) == 0:
+            if self.settings['allow-missing-steps']:
+                self.warning(
+                    'Scenario %s has missing step %s %s' %
+                    (scenario.name, step.what, step.text))
+                return
             raise cliapp.AppException(
                 'Scenario "%s", step "%s %s" has no matching '
                 'implementation' %
-- 
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