Added first layer of the echo canceller 3 functionality

webrtc/modules/audio_processing/aec3/aec3_constants_unittest.cc

Index: webrtc/modules/audio_processing/aec3/aec3_constants_unittest.cc
diff --git a/webrtc/modules/audio_processing/aec3/aec3_constants_unittest.cc b/webrtc/modules/audio_processing/aec3/aec3_constants_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..d9e84259226c54bac53ad2997d3e5a0778ec9f9a
--- /dev/null
+++ b/webrtc/modules/audio_processing/aec3/aec3_constants_unittest.cc
@@ -0,0 +1,46 @@
+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include <string>
+
+#include "webrtc/modules/audio_processing/aec3/aec3_constants.h"

[hlundin-webrtc, 2016/12/22 10:23:56]

In unit tests, the .h file associated with the code under test should be
included at the very top.
https://google.github.io/styleguide/cppguide.html#Names_and_Order_of_Includes

[peah-webrtc, 2016/12/22 16:40:03]

Thanks!
Done.

+#include "webrtc/test/gtest.h"
+
+namespace webrtc {
+
+namespace {
+
+std::string ProduceDebugText(int sample_rate_hz) {
+  std::ostringstream ss;
+  ss << "Sample rate: " << sample_rate_hz;
+  return ss.str();
+}
+
+}  // namespace
+
+TEST(BandSplitting, NumBandsForRate) {
+  EXPECT_EQ(1u, NumBandsForRate(8000));

[ivoc, 2016/12/22 13:38:13]

I think this test is fine, but a nice alternative would be a compile-time test,
since the code you're testing is constexpr. You could write something like:
static_assert(NumBandsForRate(8000) == 1);
If it somehow fails, the code will stop compiling, which I think is good,
because the earlier you catch errors the less effort they are to fix.

[peah-webrtc, 2016/12/22 16:40:03]

Great point! Done.

+  EXPECT_EQ(1u, NumBandsForRate(16000));
+  EXPECT_EQ(2u, NumBandsForRate(32000));
+  EXPECT_EQ(3u, NumBandsForRate(48000));
+}
+
+TEST(BandSplitting, LowestBandRate) {
+  {

[hlundin-webrtc, 2016/12/22 10:23:56]

Explicitly write all the test cases, like you do above. That will cost you 4
lines, while the current construct clocks in at the double.

[ivoc, 2016/12/22 13:38:13]

Why the extra braces?

[peah-webrtc, 2016/12/22 16:40:03]

Afaics those are needed for the scoped trace to ensure the correct trace output.
I have, however, removed all of these now.

Done.

[peah-webrtc, 2016/12/22 16:40:03]

Done.

+    SCOPED_TRACE(ProduceDebugText(8000));
+    EXPECT_EQ(8000, LowestBandRate(8000));
+  }
+  for (auto rate : {16000, 32000, 48000}) {
+    SCOPED_TRACE(ProduceDebugText(rate));
+    EXPECT_EQ(16000, LowestBandRate(rate));
+  }
+}
+
+}  // namespace webrtc