Introduce BackwardCodePointStateMachine to traverse chars in code points

third_party/WebKit/Source/core/editing/state_machines/BackwardCodePointStateMachineTest.cpp

Index: third_party/WebKit/Source/core/editing/state_machines/BackwardCodePointStateMachineTest.cpp
diff --git a/third_party/WebKit/Source/core/editing/state_machines/BackwardCodePointStateMachineTest.cpp b/third_party/WebKit/Source/core/editing/state_machines/BackwardCodePointStateMachineTest.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..9db55f7ae7b3e3f0d091d5a6b3ecc82edecb8f88
--- /dev/null
+++ b/third_party/WebKit/Source/core/editing/state_machines/BackwardCodePointStateMachineTest.cpp
@@ -0,0 +1,73 @@
+// 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.
+
+#include "core/editing/state_machines/BackwardCodePointStateMachine.h"
+
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace blink {
+
+namespace {
+const TextSegmentationMachineState kInvalid =
+    TextSegmentationMachineState::Invalid;
+const TextSegmentationMachineState kNeedMoreCodeUnit =
+    TextSegmentationMachineState::NeedMoreCodeUnit;
+const TextSegmentationMachineState kFinished =
+    TextSegmentationMachineState::Finished;
+}  // namespace
+
+TEST(BackwardCodePointStateMachineTest, DoNothingCase) {
+  BackwardCodePointStateMachine machine;
+  EXPECT_EQ(0, machine.getBoundaryOffset());
+}
+
+TEST(BackwardCodePointStateMachineTest, SingleCharacter) {
+  BackwardCodePointStateMachine machine;
+  EXPECT_EQ(kFinished, machine.feedPrecedingCodeUnit('a'));
+  EXPECT_EQ(-1, machine.getBoundaryOffset());
+
+  machine.reset();
+  EXPECT_EQ(kFinished, machine.feedPrecedingCodeUnit('-'));
+  EXPECT_EQ(-1, machine.getBoundaryOffset());
+
+  machine.reset();
+  EXPECT_EQ(kFinished, machine.feedPrecedingCodeUnit('\t'));
+  EXPECT_EQ(-1, machine.getBoundaryOffset());
+
+  machine.reset();
+  // U+3042 HIRAGANA LETTER A.
+  EXPECT_EQ(kFinished, machine.feedPrecedingCodeUnit(0x3042));
+  EXPECT_EQ(-1, machine.getBoundaryOffset());
+}
+
+TEST(BackwardCodePointStateMachineTest, SurrogatePair) {
+  BackwardCodePointStateMachine machine;
+
+  // U+20BB7 is \uD83D\uDDFA in UTF-16.
+  const UChar leadSurrogate = 0xD842;
+  const UChar trailSurrogate = 0xDFB7;
+
+  EXPECT_EQ(kNeedMoreCodeUnit, machine.feedPrecedingCodeUnit(trailSurrogate));
+  EXPECT_EQ(kFinished, machine.feedPrecedingCodeUnit(leadSurrogate));
+  EXPECT_EQ(-2, machine.getBoundaryOffset());
+
+  // Edge cases
+  // Unpaired trailing surrogate. Nothing to delete.
+  machine.reset();
+  EXPECT_EQ(kNeedMoreCodeUnit, machine.feedPrecedingCodeUnit(trailSurrogate));
+  EXPECT_EQ(kInvalid, machine.feedPrecedingCodeUnit('a'));
+  EXPECT_EQ(0, machine.getBoundaryOffset());
+
+  machine.reset();
+  EXPECT_EQ(kNeedMoreCodeUnit, machine.feedPrecedingCodeUnit(trailSurrogate));
+  EXPECT_EQ(kInvalid, machine.feedPrecedingCodeUnit(trailSurrogate));
+  EXPECT_EQ(0, machine.getBoundaryOffset());
+
+  // Unpaired leading surrogate. Nothing to delete.
+  machine.reset();
+  EXPECT_EQ(kInvalid, machine.feedPrecedingCodeUnit(leadSurrogate));
+  EXPECT_EQ(0, machine.getBoundaryOffset());
+}
+
+}  // namespace blink