Make NGInlineItemsBuilder construct whitespace-collapsed offset mapping

third_party/WebKit/Source/core/layout/ng/inline/ng_inline_items_builder_test.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 "core/layout/ng/inline/ng_inline_items_builder.h"
 
 #include "core/layout/LayoutInline.h"
+#include "core/layout/ng/api/ng_offset_mapping_builder.h"
 #include "core/layout/ng/inline/ng_inline_node.h"
 #include "core/style/ComputedStyle.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace blink {
 
 namespace {
 
 static PassRefPtr<ComputedStyle> CreateWhitespaceStyle(EWhiteSpace whitespace) {
   RefPtr<ComputedStyle> style(ComputedStyle::Create());
   style->SetWhiteSpace(whitespace);
   return style;
 }
 
+static String GetCollapsed(const NGOffsetMappingBuilder& builder) {
+  Vector<unsigned> mapping = builder.DumpOffsetMappingForTesting();
+
+  Vector<unsigned> collapsed_indexes;
+  for (unsigned i = 0; i + 1 < mapping.size(); ++i) {
+    if (mapping[i] == mapping[i + 1])
+      collapsed_indexes.push_back(i);
+  }
+
+  StringBuilder result;
+  result.Append('{');
+  bool first = true;
+  for (unsigned index : collapsed_indexes) {
+    if (!first)
+      result.Append(", ");
+    result.AppendNumber(index);
+    first = false;
+  }
+  result.Append('}');
+  return result.ToString();
+}
+
 class NGInlineItemsBuilderTest : public ::testing::Test {
  protected:
   void SetUp() override { style_ = ComputedStyle::Create(); }
 
   void SetWhiteSpace(EWhiteSpace whitespace) {
     style_->SetWhiteSpace(whitespace);
   }
 
   const String& TestAppend(const String inputs[], int size) {
     items_.clear();
-    NGInlineItemsBuilder builder(&items_);
+    NGOffsetMappingBuilder mapping_builder;
+    NGInlineItemsBuilder builder(&items_, &mapping_builder);
     for (int i = 0; i < size; i++)
       builder.Append(inputs[i], style_.Get());
     text_ = builder.ToString();
+    collapsed_ = GetCollapsed(mapping_builder);
     ValidateItems();
     return text_;
   }
 
   const String& TestAppend(const String& input) {
     String inputs[] = {input};
     return TestAppend(inputs, 1);
   }
 
   const String& TestAppend(const String& input1, const String& input2) {
@@ skipping 14 matching lines @@
       const NGInlineItem& item = items_[i];
       EXPECT_EQ(current_offset, item.StartOffset());
       EXPECT_LT(item.StartOffset(), item.EndOffset());
       current_offset = item.EndOffset();
     }
     EXPECT_EQ(current_offset, text_.length());
   }
 
   Vector<NGInlineItem> items_;
   String text_;
+  String collapsed_;
   RefPtr<ComputedStyle> style_;
 };
 
-#define TestWhitespaceValue(expected, input, whitespace) \
-  SetWhiteSpace(whitespace);                             \
-  EXPECT_EQ(expected, TestAppend(input)) << "white-space: " #whitespace;
+#define TestWhitespaceValue(expected_text, expected_collapsed, input,         \
+                            whitespace)                                       \
+  SetWhiteSpace(whitespace);                                                  \
+  EXPECT_EQ(expected_text, TestAppend(input)) << "white-space: " #whitespace; \
+  EXPECT_EQ(expected_collapsed, collapsed_);
 
 TEST_F(NGInlineItemsBuilderTest, CollapseSpaces) {
   String input("text text  text   text");
   String collapsed("text text text text");
-  TestWhitespaceValue(collapsed, input, EWhiteSpace::kNormal);
-  TestWhitespaceValue(collapsed, input, EWhiteSpace::kNowrap);
-  TestWhitespaceValue(collapsed, input, EWhiteSpace::kWebkitNowrap);
-  TestWhitespaceValue(collapsed, input, EWhiteSpace::kPreLine);
-  TestWhitespaceValue(input, input, EWhiteSpace::kPre);
-  TestWhitespaceValue(input, input, EWhiteSpace::kPreWrap);
+  String collapsed_indexes("{10, 16, 17}");
+  TestWhitespaceValue(collapsed, collapsed_indexes, input,
+                      EWhiteSpace::kNormal);
+  TestWhitespaceValue(collapsed, collapsed_indexes, input,
+                      EWhiteSpace::kNowrap);
+  TestWhitespaceValue(collapsed, collapsed_indexes, input,
+                      EWhiteSpace::kWebkitNowrap);
+  TestWhitespaceValue(collapsed, collapsed_indexes, input,
+                      EWhiteSpace::kPreLine);
+  TestWhitespaceValue(input, "{}", input, EWhiteSpace::kPre);
+  TestWhitespaceValue(input, "{}", input, EWhiteSpace::kPreWrap);
 }
 
 TEST_F(NGInlineItemsBuilderTest, CollapseTabs) {
-  String input("text\ttext\t text \t text");
+  String input("text text  text   text");
   String collapsed("text text text text");
-  TestWhitespaceValue(collapsed, input, EWhiteSpace::kNormal);
-  TestWhitespaceValue(collapsed, input, EWhiteSpace::kNowrap);
-  TestWhitespaceValue(collapsed, input, EWhiteSpace::kWebkitNowrap);
-  TestWhitespaceValue(collapsed, input, EWhiteSpace::kPreLine);
-  TestWhitespaceValue(input, input, EWhiteSpace::kPre);
-  TestWhitespaceValue(input, input, EWhiteSpace::kPreWrap);
+  String collapsed_indexes("{10, 16, 17}");
+  TestWhitespaceValue(collapsed, collapsed_indexes, input,
+                      EWhiteSpace::kNormal);
+  TestWhitespaceValue(collapsed, collapsed_indexes, input,
+                      EWhiteSpace::kNowrap);
+  TestWhitespaceValue(collapsed, collapsed_indexes, input,
+                      EWhiteSpace::kWebkitNowrap);
+  TestWhitespaceValue(collapsed, collapsed_indexes, input,
+                      EWhiteSpace::kPreLine);
+  TestWhitespaceValue(input, "{}", input, EWhiteSpace::kPre);
+  TestWhitespaceValue(input, "{}", input, EWhiteSpace::kPreWrap);
 }
 
 TEST_F(NGInlineItemsBuilderTest, CollapseNewLines) {
   String input("text\ntext \n text\n\ntext");
   String collapsed("text text text text");
-  TestWhitespaceValue(collapsed, input, EWhiteSpace::kNormal);
-  TestWhitespaceValue(collapsed, input, EWhiteSpace::kNowrap);
-  TestWhitespaceValue("text\ntext\ntext\n\ntext", input, EWhiteSpace::kPreLine);
-  TestWhitespaceValue(input, input, EWhiteSpace::kPre);
-  TestWhitespaceValue(input, input, EWhiteSpace::kPreWrap);
+  String collapsed_indexes("{10, 11, 17}");
+  TestWhitespaceValue(collapsed, collapsed_indexes, input,
+                      EWhiteSpace::kNormal);
+  TestWhitespaceValue(collapsed, collapsed_indexes, input,
+                      EWhiteSpace::kNowrap);
+  TestWhitespaceValue("text\ntext\ntext\n\ntext", "{9, 11}", input,
+                      EWhiteSpace::kPreLine);
+  TestWhitespaceValue(input, "{}", input, EWhiteSpace::kPre);
+  TestWhitespaceValue(input, "{}", input, EWhiteSpace::kPreWrap);
 }
 
 TEST_F(NGInlineItemsBuilderTest, CollapseNewlinesAsSpaces) {
   EXPECT_EQ("text text", TestAppend("text\ntext"));
+  EXPECT_EQ("{}", collapsed_);
   EXPECT_EQ("text text", TestAppend("text\n\ntext"));
+  EXPECT_EQ("{5}", collapsed_);
   EXPECT_EQ("text text", TestAppend("text \n\n text"));
+  EXPECT_EQ("{5, 6, 7}", collapsed_);
   EXPECT_EQ("text text", TestAppend("text \n \n text"));
+  EXPECT_EQ("{5, 6, 7, 8}", collapsed_);
 }
 
 TEST_F(NGInlineItemsBuilderTest, CollapseAcrossElements) {
   EXPECT_EQ("text text", TestAppend("text ", " text"))
       << "Spaces are collapsed even when across elements.";
+  EXPECT_EQ("{5}", collapsed_);
 }
 
 TEST_F(NGInlineItemsBuilderTest, CollapseLeadingSpaces) {
   EXPECT_EQ("text", TestAppend("  text"));
+  EXPECT_EQ("{0, 1}", collapsed_);
   EXPECT_EQ("text", TestAppend(" ", "text"));
+  EXPECT_EQ("{0}", collapsed_);
   EXPECT_EQ("text", TestAppend(" ", " text"));
+  EXPECT_EQ("{0, 1}", collapsed_);
 }
 
 TEST_F(NGInlineItemsBuilderTest, CollapseTrailingSpaces) {
   EXPECT_EQ("text", TestAppend("text  "));
+  EXPECT_EQ("{4, 5}", collapsed_);
   EXPECT_EQ("text", TestAppend("text", " "));
+  EXPECT_EQ("{4}", collapsed_);
   EXPECT_EQ("text", TestAppend("text ", " "));
+  EXPECT_EQ("{4, 5}", collapsed_);
 }
 
 TEST_F(NGInlineItemsBuilderTest, CollapseAllSpaces) {
   EXPECT_EQ("", TestAppend("  "));
+  EXPECT_EQ("{0, 1}", collapsed_);
   EXPECT_EQ("", TestAppend("  ", "  "));
+  EXPECT_EQ("{0, 1, 2, 3}", collapsed_);
   EXPECT_EQ("", TestAppend("  ", "\n"));
+  EXPECT_EQ("{0, 1, 2}", collapsed_);
   EXPECT_EQ("", TestAppend("\n", "  "));
+  EXPECT_EQ("{0, 1, 2}", collapsed_);
 }
 
 TEST_F(NGInlineItemsBuilderTest, CollapseLeadingNewlines) {
   EXPECT_EQ("text", TestAppend("\ntext"));
+  EXPECT_EQ("{0}", collapsed_);
   EXPECT_EQ("text", TestAppend("\n\ntext"));
+  EXPECT_EQ("{0, 1}", collapsed_);
   EXPECT_EQ("text", TestAppend("\n", "text"));
+  EXPECT_EQ("{0}", collapsed_);
   EXPECT_EQ("text", TestAppend("\n\n", "text"));
+  EXPECT_EQ("{0, 1}", collapsed_);
   EXPECT_EQ("text", TestAppend(" \n", "text"));
+  EXPECT_EQ("{0, 1}", collapsed_);
   EXPECT_EQ("text", TestAppend("\n", " text"));
+  EXPECT_EQ("{0, 1}", collapsed_);
   EXPECT_EQ("text", TestAppend("\n\n", " text"));
+  EXPECT_EQ("{0, 1, 2}", collapsed_);
   EXPECT_EQ("text", TestAppend(" \n", " text"));
+  EXPECT_EQ("{0, 1, 2}", collapsed_);
   EXPECT_EQ("text", TestAppend("\n", "\ntext"));
+  EXPECT_EQ("{0, 1}", collapsed_);
   EXPECT_EQ("text", TestAppend("\n\n", "\ntext"));
+  EXPECT_EQ("{0, 1, 2}", collapsed_);
   EXPECT_EQ("text", TestAppend(" \n", "\ntext"));
+  EXPECT_EQ("{0, 1, 2}", collapsed_);
 }
 
 TEST_F(NGInlineItemsBuilderTest, CollapseTrailingNewlines) {
   EXPECT_EQ("text", TestAppend("text\n"));
+  EXPECT_EQ("{4}", collapsed_);
   EXPECT_EQ("text", TestAppend("text", "\n"));
+  EXPECT_EQ("{4}", collapsed_);
   EXPECT_EQ("text", TestAppend("text\n", "\n"));
+  EXPECT_EQ("{4, 5}", collapsed_);
   EXPECT_EQ("text", TestAppend("text\n", " "));
+  EXPECT_EQ("{4, 5}", collapsed_);
   EXPECT_EQ("text", TestAppend("text ", "\n"));
+  EXPECT_EQ("{4, 5}", collapsed_);
 }
 
 TEST_F(NGInlineItemsBuilderTest, CollapseBeforeNewlineAcrossElements) {
   EXPECT_EQ("text text", TestAppend("text ", "\ntext"));
+  EXPECT_EQ("{5}", collapsed_);
   EXPECT_EQ("text text", TestAppend("text", " ", "\ntext"));
+  EXPECT_EQ("{5}", collapsed_);
 }
 
 TEST_F(NGInlineItemsBuilderTest, CollapseBeforeAndAfterNewline) {
   SetWhiteSpace(EWhiteSpace::kPreLine);
   EXPECT_EQ("text\ntext", TestAppend("text  \n  text"))
       << "Spaces before and after newline are removed.";
+  EXPECT_EQ("{4, 5, 7, 8}", collapsed_);
 }
 
 TEST_F(NGInlineItemsBuilderTest,
        CollapsibleSpaceAfterNonCollapsibleSpaceAcrossElements) {
-  NGInlineItemsBuilder builder(&items_);
+  NGOffsetMappingBuilder mapping_builder;
+  NGInlineItemsBuilder builder(&items_, &mapping_builder);
   RefPtr<ComputedStyle> pre_wrap(CreateWhitespaceStyle(EWhiteSpace::kPreWrap));
   builder.Append("text ", pre_wrap.Get());
   builder.Append(" text", style_.Get());
   EXPECT_EQ("text  text", builder.ToString())
       << "The whitespace in constructions like '<span style=\"white-space: "
          "pre-wrap\">text <span><span> text</span>' does not collapse.";
+  EXPECT_EQ("{}", GetCollapsed(mapping_builder));
 }
 
 TEST_F(NGInlineItemsBuilderTest, CollapseZeroWidthSpaces) {
   EXPECT_EQ(String(u"text\u200Btext"), TestAppend(u"text\u200B\ntext"))
       << "Newline is removed if the character before is ZWS.";
+  EXPECT_EQ("{5}", collapsed_);
   EXPECT_EQ(String(u"text\u200Btext"), TestAppend(u"text\n\u200Btext"))
       << "Newline is removed if the character after is ZWS.";
+  EXPECT_EQ("{4}", collapsed_);
   EXPECT_EQ(String(u"text\u200B\u200Btext"),
             TestAppend(u"text\u200B\n\u200Btext"))
       << "Newline is removed if the character before/after is ZWS.";
+  EXPECT_EQ("{5}", collapsed_);
 
   EXPECT_EQ(String(u"text\u200Btext"), TestAppend(u"text\n", u"\u200Btext"))
       << "Newline is removed if the character after across elements is ZWS.";
+  EXPECT_EQ("{4}", collapsed_);
   EXPECT_EQ(String(u"text\u200Btext"), TestAppend(u"text\u200B", u"\ntext"))
       << "Newline is removed if the character before is ZWS even across "
          "elements.";
+  EXPECT_EQ("{5}", collapsed_);
 
   EXPECT_EQ(String(u"text\u200Btext"), TestAppend(u"text \n", u"\u200Btext"))
       << "Collapsible space before newline does not affect the result.";
+  EXPECT_EQ("{4, 5}", collapsed_);
 
   EXPECT_EQ(String(u"text\u200Btext"), TestAppend(u"text\u200B\n", u" text"))
       << "Collapsible space after newline is removed even when the "
          "newline was removed.";
+  EXPECT_EQ("{5, 6}", collapsed_);
 }
 
 TEST_F(NGInlineItemsBuilderTest, CollapseEastAsianWidth) {
   EXPECT_EQ(String(u"\u4E00\u4E00"), TestAppend(u"\u4E00\n\u4E00"))
       << "Newline is removed when both sides are Wide.";
+  EXPECT_EQ("{1}", collapsed_);
 
   EXPECT_EQ(String(u"\u4E00 A"), TestAppend(u"\u4E00\nA"))
       << "Newline is not removed when after is Narrow.";
+  EXPECT_EQ("{}", collapsed_);
   EXPECT_EQ(String(u"A \u4E00"), TestAppend(u"A\n\u4E00"))
       << "Newline is not removed when before is Narrow.";
+  EXPECT_EQ("{}", collapsed_);
 
   EXPECT_EQ(String(u"\u4E00\u4E00"), TestAppend(u"\u4E00\n", u"\u4E00"))
       << "Newline at the end of elements is removed when both sides are Wide.";
+  EXPECT_EQ("{1}", collapsed_);
   EXPECT_EQ(String(u"\u4E00\u4E00"), TestAppend(u"\u4E00", u"\n\u4E00"))
       << "Newline at the beginning of elements is removed "
          "when both sides are Wide.";
+  EXPECT_EQ("{1}", collapsed_);
 }
 
 TEST_F(NGInlineItemsBuilderTest, OpaqueToSpaceCollapsing) {
-  NGInlineItemsBuilder builder(&items_);
+  NGOffsetMappingBuilder mapping_builder;
+  NGInlineItemsBuilder builder(&items_, &mapping_builder);
   builder.Append("Hello ", style_.Get());
   builder.AppendOpaque(NGInlineItem::kBidiControl,
                        kFirstStrongIsolateCharacter);
   builder.Append(" ", style_.Get());
   builder.AppendOpaque(NGInlineItem::kBidiControl,
                        kFirstStrongIsolateCharacter);
   builder.Append(" World", style_.Get());
   EXPECT_EQ(String(u"Hello \u2068\u2068World"), builder.ToString());
+  EXPECT_EQ("{7, 9}", GetCollapsed(mapping_builder));
 }
 
 TEST_F(NGInlineItemsBuilderTest, CollapseAroundReplacedElement) {
-  NGInlineItemsBuilder builder(&items_);
+  NGOffsetMappingBuilder mapping_builder;
+  NGInlineItemsBuilder builder(&items_, &mapping_builder);
   builder.Append("Hello ", style_.Get());
   builder.Append(NGInlineItem::kAtomicInline, kObjectReplacementCharacter);
   builder.Append(" World", style_.Get());
   EXPECT_EQ(String(u"Hello \uFFFC World"), builder.ToString());
+  EXPECT_EQ("{}", GetCollapsed(mapping_builder));
 }
 
 TEST_F(NGInlineItemsBuilderTest, CollapseNewlineAfterObject) {
-  NGInlineItemsBuilder builder(&items_);
+  NGOffsetMappingBuilder mapping_builder;
+  NGInlineItemsBuilder builder(&items_, &mapping_builder);
   builder.Append(NGInlineItem::kAtomicInline, kObjectReplacementCharacter);
   builder.Append("\n", style_.Get());
   builder.Append(NGInlineItem::kAtomicInline, kObjectReplacementCharacter);
   EXPECT_EQ(String(u"\uFFFC \uFFFC"), builder.ToString());
   EXPECT_EQ(3u, items_.size());
   EXPECT_EQ(nullptr, items_[0].Style());
   EXPECT_EQ(style_.Get(), items_[1].Style());
   EXPECT_EQ(nullptr, items_[2].Style());
+  EXPECT_EQ("{}", GetCollapsed(mapping_builder));
 }
 
 TEST_F(NGInlineItemsBuilderTest, AppendEmptyString) {
   EXPECT_EQ("", TestAppend(""));
+  EXPECT_EQ("{}", collapsed_);
   EXPECT_EQ(0u, items_.size());
 }
 
 TEST_F(NGInlineItemsBuilderTest, NewLines) {
   SetWhiteSpace(EWhiteSpace::kPre);
   EXPECT_EQ("apple\norange\ngrape\n", TestAppend("apple\norange\ngrape\n"));
+  EXPECT_EQ("{}", collapsed_);
   EXPECT_EQ(6u, items_.size());
   EXPECT_EQ(NGInlineItem::kText, items_[0].Type());
   EXPECT_EQ(NGInlineItem::kControl, items_[1].Type());
   EXPECT_EQ(NGInlineItem::kText, items_[2].Type());
   EXPECT_EQ(NGInlineItem::kControl, items_[3].Type());
   EXPECT_EQ(NGInlineItem::kText, items_[4].Type());
   EXPECT_EQ(NGInlineItem::kControl, items_[5].Type());
 }
 
 TEST_F(NGInlineItemsBuilderTest, Empty) {
   Vector<NGInlineItem> items;
-  NGInlineItemsBuilder builder(&items);
+  NGOffsetMappingBuilder mapping_builder;
+  NGInlineItemsBuilder builder(&items, &mapping_builder);
   RefPtr<ComputedStyle> block_style(ComputedStyle::Create());
   builder.EnterBlock(block_style.Get());
   builder.ExitBlock();
 
   EXPECT_EQ("", builder.ToString());
+  EXPECT_EQ("{}", GetCollapsed(mapping_builder));
 }
 
 TEST_F(NGInlineItemsBuilderTest, BidiBlockOverride) {
   Vector<NGInlineItem> items;
-  NGInlineItemsBuilder builder(&items);
+  NGOffsetMappingBuilder mapping_builder;
+  NGInlineItemsBuilder builder(&items, &mapping_builder);
   RefPtr<ComputedStyle> block_style(ComputedStyle::Create());
   block_style->SetUnicodeBidi(UnicodeBidi::kBidiOverride);
   block_style->SetDirection(TextDirection::kRtl);
   builder.EnterBlock(block_style.Get());
   builder.Append("Hello", style_.Get());
   builder.ExitBlock();
 
   // Expected control characters as defined in:
   // https://drafts.csswg.org/css-writing-modes-3/#bidi-control-codes-injection-table
   EXPECT_EQ(String(u"\u202E"
                    u"Hello"
                    u"\u202C"),
             builder.ToString());
+  EXPECT_EQ("{}", GetCollapsed(mapping_builder));
 }
 
 static std::unique_ptr<LayoutInline> CreateLayoutInline(
     void (*initialize_style)(ComputedStyle*)) {
   RefPtr<ComputedStyle> style(ComputedStyle::Create());
   initialize_style(style.Get());
   std::unique_ptr<LayoutInline> node = WTF::MakeUnique<LayoutInline>(nullptr);
   node->SetStyleInternal(std::move(style));
   return node;
 }
 
 TEST_F(NGInlineItemsBuilderTest, BidiIsolate) {
   Vector<NGInlineItem> items;
-  NGInlineItemsBuilder builder(&items);
+  NGOffsetMappingBuilder mapping_builder;
+  NGInlineItemsBuilder builder(&items, &mapping_builder);
   builder.Append("Hello ", style_.Get());
   std::unique_ptr<LayoutInline> isolate_rtl(
       CreateLayoutInline([](ComputedStyle* style) {
         style->SetUnicodeBidi(UnicodeBidi::kIsolate);
         style->SetDirection(TextDirection::kRtl);
       }));
   builder.EnterInline(isolate_rtl.get());
   builder.Append(u"\u05E2\u05D1\u05E8\u05D9\u05EA", style_.Get());
   builder.ExitInline(isolate_rtl.get());
   builder.Append(" World", style_.Get());
 
   // Expected control characters as defined in:
   // https://drafts.csswg.org/css-writing-modes-3/#bidi-control-codes-injection-table
   EXPECT_EQ(String(u"Hello "
                    u"\u2067"
                    u"\u05E2\u05D1\u05E8\u05D9\u05EA"
                    u"\u2069"
                    u" World"),
             builder.ToString());
+  EXPECT_EQ("{}", GetCollapsed(mapping_builder));
 }
 
 TEST_F(NGInlineItemsBuilderTest, BidiIsolateOverride) {
   Vector<NGInlineItem> items;
-  NGInlineItemsBuilder builder(&items);
+  NGOffsetMappingBuilder mapping_builder;
+  NGInlineItemsBuilder builder(&items, &mapping_builder);
   builder.Append("Hello ", style_.Get());
   std::unique_ptr<LayoutInline> isolate_override_rtl(
       CreateLayoutInline([](ComputedStyle* style) {
         style->SetUnicodeBidi(UnicodeBidi::kIsolateOverride);
         style->SetDirection(TextDirection::kRtl);
       }));
   builder.EnterInline(isolate_override_rtl.get());
   builder.Append(u"\u05E2\u05D1\u05E8\u05D9\u05EA", style_.Get());
   builder.ExitInline(isolate_override_rtl.get());
   builder.Append(" World", style_.Get());
 
   // Expected control characters as defined in:
   // https://drafts.csswg.org/css-writing-modes-3/#bidi-control-codes-injection-table
   EXPECT_EQ(String(u"Hello "
                    u"\u2068\u202E"
                    u"\u05E2\u05D1\u05E8\u05D9\u05EA"
                    u"\u202C\u2069"
                    u" World"),
             builder.ToString());
+  EXPECT_EQ("{}", GetCollapsed(mapping_builder));
 }
 
 }  // namespace
 
 }  // namespace blink