diff --git a/buffet/commands/dbus_command_dispatcher_unittest.cc b/buffet/commands/dbus_command_dispatcher_unittest.cc
index 170d900..9de6889 100644
--- a/buffet/commands/dbus_command_dispatcher_unittest.cc
+++ b/buffet/commands/dbus_command_dispatcher_unittest.cc
@@ -108,7 +108,7 @@
   }
 
   void FinishCommand(DBusCommandProxy* proxy) {
-    proxy->HandleDone(nullptr);
+    proxy->HandleDone();
   }
 
   void SetProgress(DBusCommandProxy* proxy, int progress) {
diff --git a/buffet/commands/dbus_command_proxy.cc b/buffet/commands/dbus_command_proxy.cc
index 0b97c06..07ead32 100644
--- a/buffet/commands/dbus_command_proxy.cc
+++ b/buffet/commands/dbus_command_proxy.cc
@@ -32,18 +32,18 @@
     dbus_object_.AddOrGetInterface(dbus_constants::kCommandInterface);
 
   // DBus methods.
-  itf->AddMethodHandler(dbus_constants::kCommandSetProgress,
-                        base::Unretained(this),
-                        &DBusCommandProxy::HandleSetProgress);
-  itf->AddMethodHandler(dbus_constants::kCommandAbort,
-                        base::Unretained(this),
-                        &DBusCommandProxy::HandleAbort);
-  itf->AddMethodHandler(dbus_constants::kCommandCancel,
-                        base::Unretained(this),
-                        &DBusCommandProxy::HandleCancel);
-  itf->AddMethodHandler(dbus_constants::kCommandDone,
-                        base::Unretained(this),
-                        &DBusCommandProxy::HandleDone);
+  itf->AddSimpleMethodHandlerWithError(dbus_constants::kCommandSetProgress,
+                                       base::Unretained(this),
+                                       &DBusCommandProxy::HandleSetProgress);
+  itf->AddSimpleMethodHandler(dbus_constants::kCommandAbort,
+                              base::Unretained(this),
+                              &DBusCommandProxy::HandleAbort);
+  itf->AddSimpleMethodHandler(dbus_constants::kCommandCancel,
+                              base::Unretained(this),
+                              &DBusCommandProxy::HandleCancel);
+  itf->AddSimpleMethodHandler(dbus_constants::kCommandDone,
+                              base::Unretained(this),
+                              &DBusCommandProxy::HandleDone);
 
   // DBus properties.
   itf->AddProperty(dbus_constants::kCommandName, &name_);
@@ -80,7 +80,7 @@
   progress_.SetValue(progress);
 }
 
-void DBusCommandProxy::HandleSetProgress(chromeos::ErrorPtr* error,
+bool DBusCommandProxy::HandleSetProgress(chromeos::ErrorPtr* error,
                                          int32_t progress) {
   LOG(INFO) << "Received call to Command<"
             << command_instance_->GetName() << ">::SetProgress("
@@ -89,24 +89,26 @@
   // Validate |progress| parameter. Its value must be between 0 and 100.
   IntPropType progress_type;
   progress_type.AddMinMaxConstraint(0, 100);
-  if (progress_type.ValidateValue(progress, error)) {
-    command_instance_->SetProgress(progress);
-  }
+  if (!progress_type.ValidateValue(progress, error))
+    return false;
+
+  command_instance_->SetProgress(progress);
+  return true;
 }
 
-void DBusCommandProxy::HandleAbort(chromeos::ErrorPtr* error) {
+void DBusCommandProxy::HandleAbort() {
   LOG(INFO) << "Received call to Command<"
             << command_instance_->GetName() << ">::Abort()";
   command_instance_->Abort();
 }
 
-void DBusCommandProxy::HandleCancel(chromeos::ErrorPtr* error) {
+void DBusCommandProxy::HandleCancel() {
   LOG(INFO) << "Received call to Command<"
             << command_instance_->GetName() << ">::Cancel()";
   command_instance_->Cancel();
 }
 
-void DBusCommandProxy::HandleDone(chromeos::ErrorPtr* error) {
+void DBusCommandProxy::HandleDone() {
   LOG(INFO) << "Received call to Command<"
             << command_instance_->GetName() << ">::Done()";
   command_instance_->Done();
diff --git a/buffet/commands/dbus_command_proxy.h b/buffet/commands/dbus_command_proxy.h
index 553470e..50878fb 100644
--- a/buffet/commands/dbus_command_proxy.h
+++ b/buffet/commands/dbus_command_proxy.h
@@ -50,13 +50,13 @@
       parameters_;
 
   // Handles calls to org.chromium.Buffet.Command.SetProgress(progress).
-  void HandleSetProgress(chromeos::ErrorPtr* error, int32_t progress);
+  bool HandleSetProgress(chromeos::ErrorPtr* error, int32_t progress);
   // Handles calls to org.chromium.Buffet.Command.Abort().
-  void HandleAbort(chromeos::ErrorPtr* error);
+  void HandleAbort();
   // Handles calls to org.chromium.Buffet.Command.Cancel().
-  void HandleCancel(chromeos::ErrorPtr* error);
+  void HandleCancel();
   // Handles calls to org.chromium.Buffet.Command.Done().
-  void HandleDone(chromeos::ErrorPtr* error);
+  void HandleDone();
 
   dbus::ObjectPath object_path_;
   CommandInstance* command_instance_;
diff --git a/buffet/commands/dbus_command_proxy_unittest.cc b/buffet/commands/dbus_command_proxy_unittest.cc
index f8fba8d..ae91b13 100644
--- a/buffet/commands/dbus_command_proxy_unittest.cc
+++ b/buffet/commands/dbus_command_proxy_unittest.cc
@@ -9,6 +9,7 @@
 #include <dbus/mock_exported_object.h>
 #include <dbus/property.h>
 #include <chromeos/dbus/dbus_object.h>
+#include <chromeos/dbus/dbus_object_test_helpers.h>
 #include <gtest/gtest.h>
 
 #include "buffet/commands/command_dictionary.h"
@@ -131,8 +132,8 @@
     dbus::MessageWriter writer(&method_call);
     if (param_callback)
       param_callback(&writer);
-    return chromeos::dbus_utils::CallMethod(*GetProxyDBusObject(),
-                                            &method_call);
+    return chromeos::dbus_utils::testing::CallMethod(*GetProxyDBusObject(),
+                                                     &method_call);
   }
 
   static bool IsResponseError(const std::unique_ptr<dbus::Response>& response) {
@@ -157,8 +158,8 @@
     dbus::MessageWriter writer(&method_call);
     writer.AppendString(dbus_constants::kCommandInterface);
     writer.AppendString(property_name);
-    auto response = chromeos::dbus_utils::CallMethod(*GetProxyDBusObject(),
-                                                     &method_call);
+    auto response = chromeos::dbus_utils::testing::CallMethod(
+        *GetProxyDBusObject(), &method_call);
     T value{};
     VerifyResponse(response, [&value](dbus::MessageReader* reader) {
       EXPECT_TRUE(chromeos::dbus_utils::PopValueFromReader(reader, &value));