Adding mediator for Sign-in promo

ios/chrome/browser/ui/authentication/signin_promo_view_unittest.mm

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#import "ios/chrome/browser/ui/authentication/signin_promo_view.h"
+
+#import "ios/third_party/material_components_ios/src/components/Buttons/src/MaterialButtons.h"
+#include "third_party/ocmock/gtest_support.h"
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+TEST(SigninPromoViewTest, SecondaryButtonVisibility) {
+  SigninPromoView* view =
+      [[SigninPromoView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
+  view.mode = SigninPromoViewModeColdState;
+  EXPECT_TRUE(view.secondaryButton.hidden);
+  view.mode = SigninPromoViewModeWarmState;
+  EXPECT_FALSE(view.secondaryButton.hidden);
+}