Add resilience in croc to a failed build (e.g. 0 stats generated)....

tools/code_coverage/croc_test.py

 #!/usr/bin/python2.4
 #
 # Copyright 2009, Google Inc.
 # All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #        * Redistributions of source code must retain the above copyright
@@ skipping 632 matching lines @@
     # Include files from the main dir and subdir
     self.assertEqual(sorted(c.files), [
         '_/proj1/a.c',
         '_/proj1/subdir/cherry.c',
         '_/proj1/yes.c'])
 
     # Excluded dir should have been pruned from the mock walk data dirnames.
     # In the real os.walk() call this prunes the walk.
     self.assertEqual(self.mock_walk_return[0][1], ['subdir'])
 
+
+  def testEmptyTreeStats(self):
+    """Make sure we don't choke when absolutely nothing happened.
+
+    How we might hit this: bot compile error."""
+    c = self.cov_minimal
+    t = c.tree
+    t.stats_by_group['all'].AddDefaults()
+    self.assertEqual(t.stats_by_group, {
+        'all': { 'files_covered': 0,
+                 'files_instrumented': 0,
+                 'files_executable': 0,
+                 'lines_covered': 0,
+                 'lines_instrumented': 0,
+                 'lines_executable': 0 }})
+
   def testUpdateTreeStats(self):
     """Test UpdateTreeStats()."""
 
     c = self.cov_minimal
     c.AddRule('.*_test', group='test')
 
     # Fill the files list
     c.ParseLcovData([
         'SF:/src/a.c',
         'DA:10,1', 'DA:11,1', 'DA:20,0',
@@ skipping 105 matching lines @@
   # TODO: test: less important, since these are thin wrappers around other
   # tested methods.
   #     ParseConfig()
   #     ParseLcovFile()
   #     PrintTree()
 
 #------------------------------------------------------------------------------
 
 if __name__ == '__main__':
   unittest.main()