Index: test/lit.common.cfg
===================================================================
--- test/lit.common.cfg
+++ test/lit.common.cfg
@@ -157,7 +157,12 @@
   config.substitutions.append(('%device_rm', '{} rm '.format(run_wrapper)))
   config.compile_wrapper = compile_wrapper
 
-  prepare_output = subprocess.check_output([prepare_script, config.apple_platform, config.clang]).strip()
+  try:
+    prepare_output = subprocess.check_output([prepare_script, config.apple_platform, config.clang]).strip()
+  except subprocess.CalledProcessError as e:
+    print("Command failed:")
+    print(e.output)
+    raise e
   if len(prepare_output) > 0: print(prepare_output)
   prepare_output_json = prepare_output.split("\n")[-1]
   prepare_output = json.loads(prepare_output_json)