Let expect_tests stop walking across certain packages.

expect_tests/main.py

Index: expect_tests/main.py
diff --git a/expect_tests/main.py b/expect_tests/main.py
index 238c38c38c9abc6c7989796ec0ce914744818d10..a9400f96e3b1796ec002d03c1511d6024a83c028 100644
--- a/expect_tests/main.py
+++ b/expect_tests/main.py
@@ -134,8 +134,15 @@ def find_all_modules():
   sys.path.insert(0, '.')
 
   ret = []
+  blacklist = set()
   for importer, modname, ispkg in pkgutil.walk_packages(path=['.']):
-    if not ispkg and modname.endswith('_test'):
+    if ispkg and getattr(importer.find_module(modname).load_module(modname),
+                         '_expect_tests_stop_walk', False):
+        blacklist.add(modname)
+      continue
+    if modname.endswith('_test'):
+      if any(modname.startswith(pkg) for pkg in blacklist):
+        continue
       if modname in sys.modules:
         ret.append(sys.modules[modname])
       else: