diff --git a/tools/test.py b/tools/test.py
index b92c8dc..6c15ea5 100755
--- a/tools/test.py
+++ b/tools/test.py
@@ -100,6 +100,8 @@
 
 def Main():
   (options, args) = ParseOptions()
+  if 'BUILDBOT_BUILDERNAME' in os.environ:
+    gradle.RunGradle(['clean'])
 
   gradle_args = ['--stacktrace']
   # Set all necessary Gradle properties and options first.