Blimp: add delta encoding family of functions

blimp/net/delta_encoding_unittest.cc

+// Copyright 2016 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 "blimp/net/delta_encoding.h"
+
+#include <string>
+#include <vector>
+
+#include "base/logging.h"
+#include "base/macros.h"
+#include "testing/gmock/include/gmock/gmock.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+using testing::ElementsAre;
+
+namespace blimp {
+namespace {
+
+struct CompoundStruct {

[nyquist, 2016/08/26 20:43:42]

Could you add a clarifying comment as to how strings are encoded here so I
wouldn't necessarily have to fine-parse the code?
I think that would help me read the tests later.

[Wez, 2016/08/29 23:25:24]

+1 :)

[Kevin M, 2016/08/30 19:06:33]

Done.

+  static CompoundStruct Difference(const CompoundStruct& lhs,
+                                   const CompoundStruct& rhs) {
+    CompoundStruct output;
+    output.number = lhs.number - rhs.number;
+    if (lhs.str != rhs.str) {
+      output.str = lhs.str;
+    }
+    return output;
+  }
+
+  static CompoundStruct Merge(const CompoundStruct& lhs,
+                              const CompoundStruct& rhs) {
+    CompoundStruct output;
+    output.number = lhs.number + rhs.number;
+    output.str = (rhs.str.empty() ? lhs.str : rhs.str);
+    return output;
+  }
+
+  int number;
+  std::string str;
+};
+
+class TestDeltaEncoding : public testing::Test {
+ public:
+  TestDeltaEncoding() {}
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(TestDeltaEncoding);
+};
+
+TEST_F(TestDeltaEncoding, DeltaEncode) {
+  std::vector<int> test{5, 1, 3};
+  DeltaEncode(test.begin(), test.end());
+  EXPECT_THAT(test, ElementsAre(5, -4, 2));
+}
+
+TEST_F(TestDeltaEncoding, DeltaEncodeEmpty) {
+  std::vector<int> test;
+  DeltaEncode(test.begin(), test.end());
+  EXPECT_TRUE(test.empty());
+}
+
+TEST_F(TestDeltaEncoding, DeltaEncodeSingleValue) {
+  std::vector<int> test;
+  test.push_back(1);
+  DeltaEncode(test.begin(), test.end());
+  EXPECT_THAT(test, ElementsAre(1));
+}
+
+TEST_F(TestDeltaEncoding, DeltaDecode) {
+  std::vector<int> test{1, 1, 2};
+  DeltaDecode(test.begin(), test.end());
+  EXPECT_THAT(test, ElementsAre(1, 2, 4));
+}
+
+TEST_F(TestDeltaEncoding, DeltaDecodeEmpty) {
+  std::vector<int> test;
+  DeltaDecode(test.begin(), test.end());
+  EXPECT_TRUE(test.empty());
+}
+
+TEST_F(TestDeltaEncoding, DeltaDecodeSingleValue) {
+  std::vector<int> test{1};
+  DeltaEncode(test.begin(), test.end());
+  EXPECT_THAT(test, ElementsAre(1));
+}
+
+TEST_F(TestDeltaEncoding, SortAndDeltaEncodeRoundTrip) {
+  std::vector<int> test{8, 3, 5};
+  SortAndDeltaEncode(test.begin(), test.end());
+  EXPECT_THAT(test, ElementsAre(3, 2, 3));
+  DeltaDecode(test.begin(), test.end());
+  EXPECT_THAT(test, ElementsAre(3, 5, 8));
+}
+
+TEST_F(TestDeltaEncoding, DeltaEncodeStruct) {
+  std::vector<CompoundStruct> test{{2, "foo"}, {3, "foo"}, {0, "bar"}};
+  DeltaEncode(test.begin(), test.end(), &CompoundStruct::Difference);
+
+  EXPECT_EQ(2, test[0].number);
+  EXPECT_EQ(1, test[1].number);
+  EXPECT_EQ(-3, test[2].number);
+
+  EXPECT_EQ("foo", test[0].str);
+  EXPECT_EQ("", test[1].str);
+  EXPECT_EQ("bar", test[2].str);
+}
+
+TEST_F(TestDeltaEncoding, DeltaDecodeStruct) {

[nyquist, 2016/08/26 20:43:42]

How does a sortable compound struct work? Could you add a test for that so it's
easy to understand how to do something like that?

[Kevin M, 2016/08/30 19:06:33]

You would pick some kind of key field and sort using that. I added a test that
sorts based on |CompoundStruct::number|.

+  std::vector<CompoundStruct> test{{2, "foo"}, {-1, ""}, {0, "bar"}};
+  DeltaDecode(test.begin(), test.end(), &CompoundStruct::Merge);
+
+  EXPECT_EQ(2, test[0].number);
+  EXPECT_EQ(1, test[1].number);
+  EXPECT_EQ(1, test[2].number);
+
+  EXPECT_EQ("foo", test[0].str);
+  EXPECT_EQ("foo", test[1].str);
+  EXPECT_EQ("bar", test[2].str);
+}
+
+}  // namespace
+}  // namespace blimp