Bug 1182817 - [manifestparser] Fix exception in chunk_by_slice when there are two times more chunks than tests, r=chmanchester

--HG--
extra : commitid : K5KnytkByDT
extra : rebase_source : 502b560240f8319b3955485578705a5319980992

testing/mozbase/manifestparser/manifestparser/filters.py

@@ -183,12 +183,12 @@ class chunk_by_slice(InstanceFilter):
             # chunk will contain an equal number of enabled tests.
             if self.this_chunk == 1:
                 start = 0
-            else:
+            elif start < len(chunk_tests):
                 start = tests.index(chunk_tests[start])
 
             if self.this_chunk == self.total_chunks:
                 end = len(tests)
-            else:
+            elif end < len(chunk_tests):
                 end = tests.index(chunk_tests[end])
         return (t for t in tests[start:end])
 

testing/mozbase/manifestparser/tests/test_chunking.py

@@ -66,6 +66,15 @@ class ChunkBySlice(TestCase):
         disabled = list(i for i in xrange(num_tests) if i % 4 == 0)
         self.run_all_combos(num_tests=num_tests, disabled=disabled)
 
+    def test_two_times_more_chunks_than_tests(self):
+        # test case for bug 1182817
+        tests = self.generate_tests(5)
+
+        total_chunks = 10
+        for i in range(1, total_chunks + 1):
+            # ensure IndexError is not raised
+            chunk_by_slice(i, total_chunks)(tests, {})
+
 
 class ChunkByDir(TestCase):
     """Test chunking related filters"""