fixing exclusionary tags behavior

lettuce/core.py

@@ -583,14 +583,19 @@ class Scenario(object):
         if tags is None:
             return True
 
-        if not self.tags:
+        has_exclusionary_tags = any([t.startswith('-') for t in tags])
+
+        if not self.tags and not has_exclusionary_tags:
             return False
 
         matched = []
 
-        for tag in self.tags:
-            if tag in tags:
-                return True
+        if isinstance(self.tags, list):
+            for tag in self.tags:
+                if tag in tags:
+                    return True
+        else:
+            self.tags = []
 
         for tag in tags:
             exclude = tag.startswith('-')

tests/unit/test_scenario_parsing.py

@@ -497,6 +497,17 @@ def test_scenario_matches_tags_excluding():
     assert scenario.matches_tags(['-foobar'])
 
 
+def test_scenario_matches_tags_excluding_when_scenario_has_no_tags():
+    ("When Scenario#matches_tags is called for a scenario "
+     "that has no tags and the given match is a exclusionary tag")
+
+    scenario = Scenario.from_string(
+        SCENARIO1,
+        original_string=(SCENARIO1.strip()))
+
+    assert scenario.matches_tags(['-nope', '-neither'])
+
+
 def test_scenario_matches_tags_excluding_fuzzywuzzy():
     ("When Scenario#matches_tags is called with a member starting with -~ "
      "it will exclude that tag from that fuzzywuzzy match")