Print a warning if the directory passed to --test-subdir doesn't end up existing

llvm-svn: 276709

lldb/packages/Python/lldbsuite/test/dosep.py

@@ -1515,6 +1515,8 @@ def main(num_threads, test_subdir, test_runner_name, results_formatter):
     test_directory = os.path.dirname(os.path.realpath(__file__))
     if test_subdir and len(test_subdir) > 0:
         test_subdir = os.path.join(test_directory, test_subdir)
+        if not os.path.isdir(test_subdir):
+          print('specified test subdirectory {} is not a valid directory\n'.format(test_subdir))
     else:
         test_subdir = test_directory