diff --git a/tools/releasetools/test_utils.py b/tools/releasetools/test_utils.py
index ca127b1..1e919f7 100755
--- a/tools/releasetools/test_utils.py
+++ b/tools/releasetools/test_utils.py
@@ -31,6 +31,18 @@
 # Some test runner doesn't like outputs from stderr.
 logging.basicConfig(stream=sys.stdout)
 
+# Use ANDROID_BUILD_TOP as an indicator to tell if the needed tools (e.g.
+# avbtool, mke2fs) are available while running the tests. Not having the var or
+# having empty string means we can't run the tests that require external tools.
+EXTERNAL_TOOLS_UNAVAILABLE = not os.environ.get("ANDROID_BUILD_TOP")
+
+
+def SkipIfExternalToolsUnavailable():
+  """Decorator function that allows skipping tests per tools availability."""
+  if EXTERNAL_TOOLS_UNAVAILABLE:
+    return unittest.skip('External tools unavailable')
+  return lambda func: func
+
 
 def get_testdata_dir():
   """Returns the testdata dir, in relative to the script dir."""