Add helpers for logging mojom objects.

mojo/public/cpp/bindings/tests/array_unittest.cc

 // Copyright 2014 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.
 
 #include "mojo/public/cpp/bindings/array.h"
 #include "mojo/public/cpp/bindings/lib/array_internal.h"
 #include "mojo/public/cpp/bindings/lib/array_serialization.h"
 #include "mojo/public/cpp/bindings/lib/fixed_buffer.h"
 #include "mojo/public/cpp/bindings/tests/container_test_util.h"
 #include "mojo/public/cpp/bindings/tests/iterator_test_util.h"
@@ skipping 810 matching lines @@
     EXPECT_EQ(-3, array3[0]->width);
     EXPECT_EQ(-4, array3[0]->height);
     EXPECT_FALSE(array3[1].is_null());
     EXPECT_EQ(1, array3[1]->x);
     EXPECT_EQ(2, array3[1]->y);
     EXPECT_EQ(3, array3[1]->width);
     EXPECT_EQ(4, array3[1]->height);
   }
 }
 
+TEST_F(ArrayTest, OutputFormatting) {
+  Array<int32_t> null_array;
+  Array<int32_t> empty_array;
+  empty_array.resize(0);
+  Array<int32_t> one_element_array;
+  one_element_array.push_back(123);
+  Array<int32_t> three_element_array;
+  three_element_array.push_back(4);
+  three_element_array.push_back(5);
+  three_element_array.push_back(6);
+
+  std::ostringstream so;
+  so << "null_array=" << null_array << ", empty_array=" << empty_array
+     << ", one_element_array=" << one_element_array
+     << ", three_element_array=" << three_element_array;
+
+  EXPECT_EQ(
+      "null_array=null, "
+      "empty_array=[], "
+      "one_element_array=[123], "
+      "three_element_array=[4, 5, 6]",
+      so.str());
+}
+
 }  // namespace
 }  // namespace test
 }  // namespace mojo