AU: Try to remove unit test flakiness on buildbots.

test_utils.h

 // Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_TEST_UTILS_H__
 #define CHROMEOS_PLATFORM_UPDATE_ENGINE_TEST_UTILS_H__
 
 #include <set>
 #include <string>
 #include <vector>
@@ skipping 90 matching lines @@
 // parent. Also, verifies that no additional paths are present under parent.
 // Also tests properties of various files created by CreateExtImageAtPath().
 // Intentionally copies expected_paths.
 void VerifyAllPaths(const std::string& parent,
                     std::set<std::string> expected_paths);
 
 class ScopedLoopbackDeviceReleaser {
  public:
   explicit ScopedLoopbackDeviceReleaser(const std::string& dev) : dev_(dev) {}
   ~ScopedLoopbackDeviceReleaser() {
-    std::vector<std::string> args;
-    args.push_back("/sbin/losetup");
-    args.push_back("-d");
-    args.push_back(dev_);
-    int return_code = 0;
-    EXPECT_TRUE(Subprocess::SynchronousExec(args, &return_code));
-    EXPECT_EQ(0, return_code);
+    for (int retry = 0; retry < 5; retry++) {
+      std::vector<std::string> args;
+      args.push_back("/sbin/losetup");
+      args.push_back("-d");
+      args.push_back(dev_);
+      int return_code = 0;
+      EXPECT_TRUE(Subprocess::SynchronousExec(args, &return_code));
+      if (return_code == 0) {
+        return;
+      }
+      sleep(1);
+    }
+    ADD_FAILURE();
   }
  private:
   const std::string dev_;
   DISALLOW_COPY_AND_ASSIGN(ScopedLoopbackDeviceReleaser);
 };
 
 class ScopedTempFile {
  public:
   ScopedTempFile() {
     EXPECT_TRUE(utils::MakeTempFile("/tmp/update_engine_test_temp_file.XXXXXX",
@@ skipping 73 matching lines @@
   static std::string StaticType() { return "ObjectCollectorAction"; }
   std::string Type() const { return StaticType(); }
   const T& object() const { return object_; }
  private:
   T object_;
 };
 
 }  // namespace chromeos_update_engine
 
 #endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_TEST_UTILS_H__