Fix return value of new slave-distribution function

scripts/master/unittests/master_utils_test.py

 #!/usr/bin/env python
 # Copyright 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Source file for master_utils testcases."""
 
 
 import unittest
 
@@ skipping 78 matching lines @@
         MockSlaveBuilder('s2', {'preferred_builder': 'builder2'}),
         MockSlaveBuilder('s3', {'preferred_builder': 'builder3'}),
         MockSlaveBuilder('s4', {'preferred_builder': 'builder1'}),
         MockSlaveBuilder('s5', {'preferred_builder': 'builder2'}),
         MockSlaveBuilder('s6', {'preferred_builder': 'builder3'}),
         # Fall-over pool with no preference.
         MockSlaveBuilder('s7', {'preferred_builder': None}),
         MockSlaveBuilder('s8', {'preferred_builder': None}),
     ]
 
-    # Mock random.choice on function return for determinism and to check the
-    # full choice range.
-    f = lambda builder, slaves: (
-        set([s.name for s in master_utils.PreferredBuilderNextSlaveFuncNG(
-            choice=list)(builder, slaves)]))
+    def f(builder, slaves):
+      # Call original method for code coverage only.
+      master_utils.PreferredBuilderNextSlaveFuncNG()(builder, slaves)
+
+      # Mock random.choice on function return for determinism and to check the
+      # full choice range.
+      mocked_func = master_utils.PreferredBuilderNextSlaveFuncNG(choice=list)
+      return set([s.name for s in mocked_func(builder, slaves)])
 
     self.assertEqual(set(['s1', 's4']), f(builder1, slaves))
     self.assertEqual(set(['s2', 's5']), f(builder2, slaves))
     self.assertEqual(set(['s3', 's6']), f(builder3, slaves))
 
     remove_slave(slaves, 's3')
 
     # There's still a preferred slave left.
     self.assertEqual(set(['s6']), f(builder3, slaves))
 
@@ skipping 17 matching lines @@
   def testNextSlaveEmptyNG(self):
     builder = MockBuilder('builder')
     slaves = []
 
     f = master_utils.PreferredBuilderNextSlaveFuncNG(choice=list)
 
     self.assertIsNone(f(builder, slaves))
 
 if __name__ == '__main__':
   unittest.main()