Get test running scripts to detect and report common error.

testing/tools/run_corpus_tests.py

 #!/usr/bin/env python
 # Copyright 2015 The PDFium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import optparse
 import os
 import re
 import shutil
 import subprocess
@@ skipping 24 matching lines @@
     return False
   return True
 
 def main():
   parser = optparse.OptionParser()
   parser.add_option('--build-dir', default=os.path.join('out', 'Debug'),
                     help='relative path from the base source directory')
   options, args = parser.parse_args()
   finder = common.DirectoryFinder(options.build_dir)
   pdfium_test_path = finder.ExecutablePath('pdfium_test')
+  if not os.path.exists(pdfium_test_path):
+    print "FAILURE: Can't find test executable '%s'" % pdfium_test_path
+    print "Use --build-dir to specify its location."
+    return 1
   working_dir = finder.WorkingDir(os.path.join('testing', 'corpus'))
   if not os.path.exists(working_dir):
     os.makedirs(working_dir)
 
   test_suppressor = suppressor.Suppressor(finder)
   image_differ = pngdiffer.PNGDiffer(finder)
 
   # test files are under .../pdfium/testing/corpus.
   failures = []
   walk_from_dir = finder.TestingDir('corpus');
@@ skipping 13 matching lines @@
     print '\n\nSummary of Failures:'
     for failure in failures:
       print failure
     return 1
 
   return 0
 
 
 if __name__ == '__main__':
   sys.exit(main())