SAMPLE: Copy files

third_party/WebKit/LayoutTests/editing/foo.js

Index: third_party/WebKit/LayoutTests/editing/foo.js
diff --git a/third_party/WebKit/LayoutTests/editing/foo.js b/third_party/WebKit/LayoutTests/editing/foo.js
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+// 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.
+
+'use strict';
+
+// This file provides |assert_selection(sample, tester, expectedText, options)|
+// assertion to W3C test harness to write editing test cases easier.
+//
+// |sample| is an HTML fragment text which is inserted as |innerHTML|. It should
+// have at least one focus boundary point marker "|" and at most one anchor
+// boundary point marker "^".
+//
+// |tester| is either name with parameter of execCommand or function taking
+// one parameter |Selection|.
+//
+// |expectedText| is an HTML fragment text containing at most one focus marker
+// and anchor marker. If resulting selection is none, you don't need to have
+// anchor and focus markers.
+//
+// |options| is a string as description, undefined, or a dictionary containing:
+//  description: A description
+//  dumpAs: 'domtree' or 'flattree'. Default is 'domtree'.
+//  removeSampleIfSucceeded: A boolean. Default is true.
+//
+// Example:
+//  test(() => {
+//    assert_selection(
+//      '|foo',
+//      (selection) => selection.modify('extent', 'forward, 'character'),
+//      '<a href="http://bar">^f|oo</a>'
+//  });
+//
+//  test(() => {
+//    assert_selection(
+//      'x^y|z',
+//      'bold',  // execCommand name as a test
+//      'x<b>y</b>z',
+//      'Insert B tag');
+//  });
+//
+//  test(() => {
+//    assert_selection(
+//      'x^y|z',
+//      'createLink http://foo',  // execCommand name and parameter
+//      'x<a href="http://foo/">y</a></b>z',
+//      'Insert B tag');
+//  });
+//
+//
+
+// TODO(yosin): Please use "clang-format -style=Chromium -i" for formatting
+// this file.
+
+(function() {
+  /** @enum{string} */
+  const DumpAs = {
+    DOM_TREE: 'domtree',
+    FLAT_TREE: 'flattree',
+  };
+
+  /** @const @type {string} */
+  const kTextArea = 'TEXTAREA';
+
+  class Traversal {
+    /**
+   * @param {!Node} node
+   * @return {Node}
+   */
+    firstChildOf(node) { throw new Error('You should implement firstChildOf'); }
+
+    /**
+   * @param {!Node} node
+   * @return {!Generator<Node>}
+   */
+    * childNodesOf(node) {
+      for (let child = this.firstChildOf(node); child !== null;
+           child = this.nextSiblingOf(child)) {
+        yield child;
+      }
+    }
+
+    /**
+   * @param {!DOMSelection} selection
+   * @return !SampleSelection
+   */
+    fromDOMSelection(selection) {
+      throw new Error('You should implement fromDOMSelection');
+    }
+
+    /**
+   * @param {!Node} node
+   * @return {Node}
+   */
+    nextSiblingOf(node) {
+      throw new Error('You should implement nextSiblingOf');
+    }
+  }
+
+  class DOMTreeTraversal extends Traversal {
+    /**
+   * @override
+   * @param {!Node} node
+   * @return {Node}
+   */
+    firstChildOf(node) { return node.firstChild; }
+
+    /**
+   * @param {!DOMSelection} selection
+   * @return !SampleSelection
+   */
+    fromDOMSelection(selection) {
+      return SampleSelection.fromDOMSelection(selection);
+    }
+
+    /**
+   * @param {!Node} node
+   * @return {Node}
+   */
+    nextSiblingOf(node) { return node.nextSibling; }
+  };
+
+  class FlatTreeTraversal extends Traversal {
+    /**
+   * @override
+   * @param {!Node} node
+   * @return {Node}
+   */
+    firstChildOf(node) { return internals.firstChildInFlatTree(node); }
+
+    /**
+   * @param {!DOMSelection} selection
+   * @return !SampleSelection
+   */
+    fromDOMSelection(selection) {
+      // TODO(yosin): We should return non-scoped selection rather than
+      // selection
+      // scoped in main tree.
+      return SampleSelection.fromDOMSelection(selection);
+    }
+
+    /**
+   * @param {!Node} node
+   * @return {Node}
+   */
+    nextSiblingOf(node) { return internals.nextSiblingInFlatTree(node); }
+  }
+
+  /**
+ * @param {!Node} node
+ * @return {boolean}
+ */
+  function isCharacterData(node) {
+    return node.nodeType === Node.TEXT_NODE ||
+        node.nodeType === Node.COMMENT_NODE;
+  }
+
+  /**
+ * @param {!Node} node
+ * @return {boolean}
+ */
+  function isElement(node) { return node.nodeType === Node.ELEMENT_NODE; }
+
+  /**
+   * @param {!Node} node
+   * @param {number} offset
+   */
+  function checkValidNodeAndOffset(node, offset) {
+    if (!node)
+      throw new Error('Node parameter should not be a null.');
+    if (offset < 0)
+      throw new Error(`Assumes ${offset} >= 0`);
+    if (isElement(node)) {
+      if (offset > node.childNodes.length)
+        throw new Error(`Bad offset ${offset} for ${node}`);
+      return;
+    }
+    if (isCharacterData(node)) {
+      if (offset > node.nodeValue.length)
+        throw new Error(`Bad offset ${offset} for ${node}`);
+      return;
+    }
+    throw new Error(`Invalid node: ${node}`);
+  }
+
+  class SampleSelection {
+    /** @public */
+    constructor() {
+      /** @type {?Node} */
+      this.anchorNode_ = null;
+      /** @type {number} */
+      this.anchorOffset_ = 0;
+      /** @type {?Node} */
+      this.focusNode_ = null;
+      /** @type {number} */
+      this.focusOffset_ = 0;
+      /** @type {HTMLElement} */
+      this.shadowHost_ = null;
+    }
+
+    /**
+     * @public
+     * @param {!Node} node
+     * @param {number} offset
+     */
+    collapse(node, offset) {
+      checkValidNodeAndOffset(node, offset);
+      this.anchorNode_ = this.focusNode_ = node;
+      this.anchorOffset_ = this.focusOffset_ = offset;
+    }
+
+    /**
+     * @public
+     * @param {!Node} node
+     * @param {number} offset
+     */
+    extend(node, offset) {
+      checkValidNodeAndOffset(node, offset);
+      this.focusNode_ = node;
+      this.focusOffset_ = offset;
+    }
+
+    /** @public @return {?Node} */
+    get anchorNode() {
+      console.assert(!this.isNone, 'Selection should not be a none.');
+      return this.anchorNode_;
+    }
+    /** @public @return {number} */
+    get anchorOffset() {
+      console.assert(!this.isNone, 'Selection should not be a none.');
+      return this.anchorOffset_;
+    }
+    /** @public @return {?Node} */
+    get focusNode() {
+      console.assert(!this.isNone, 'Selection should not be a none.');
+      return this.focusNode_;
+    }
+    /** @public @return {number} */
+    get focusOffset() {
+      console.assert(!this.isNone, 'Selection should not be a none.');
+      return this.focusOffset_;
+    }
+
+    /** @public @return {HTMLElement} */
+    get shadowHost() { return this.shadowHost_; }
+
+    /**
+   * @public
+   * @return {boolean}
+   */
+    get isCollapsed() {
+      return this.anchorNode === this.focusNode &&
+          this.anchorOffset === this.focusOffset;
+    }
+
+    /**
+   * @public
+   * @return {boolean}
+   */
+    get isNone() { return this.anchorNode_ === null; }
+
+    /**
+   * @public
+   * @param {!Selection} domSelection
+   * @return {!SampleSelection}
+   */
+    static fromDOMSelection(domSelection) {
+      /** type {!SampleSelection} */
+      const selection = new SampleSelection();
+      selection.anchorNode_ = domSelection.anchorNode;
+      selection.anchorOffset_ = domSelection.anchorOffset;
+      selection.focusNode_ = domSelection.focusNode;
+      selection.focusOffset_ = domSelection.focusOffset;
+
+      if (selection.anchorNode_ === null)
+        return selection;
+
+      const document = selection.anchorNode_.ownerDocument;
+      selection.shadowHost_ = (() => {
+        if (!document.activeElement)
+          return null;
+        if (document.activeElement.nodeName !== kTextArea)
+          return null;
+        const selectedNode =
+            selection.anchorNode.childNodes[selection.anchorOffset];
+        if (document.activeElement !== selectedNode)
+          return null;
+        return selectedNode;
+      })();
+      return selection;
+    }
+
+    /** @override */
+    toString() {
+      if (this.isNone)
+        return 'SampleSelection()';
+      if (this.isCollapsed)
+        return `SampleSelection(${this.focusNode_}@${this.focusOffset_})`;
+      return `SampleSelection(anchor: ${this.anchorNode_}@${this.anchorOffset_
+          }` +
+          `focus: ${this.focusNode_}@${this.focusOffset_}`;
+    }
+  }
+
+  // Extracts selection from marker "^" as anchor and "|" as focus from
+  // DOM tree and removes them.
+  class Parser {
+    /** @private */
+    constructor() {
+      /** @type {?Node} */
+      this.anchorNode_ = null;
+      /** @type {number} */
+      this.anchorOffset_ = 0;
+      /** @type {?Node} */
+      this.focusNode_ = null;
+      /** @type {number} */
+      this.focusOffset_ = 0;
+    }
+
+    /**
+   * @public
+   * @return {!SampleSelection}
+   */
+    get selection() {
+      const selection = new SampleSelection();
+      if (!this.anchorNode_ && !this.focusNode_)
+        return selection;
+      if (this.anchorNode_ && this.focusNode_) {
+        selection.collapse(this.anchorNode_, this.anchorOffset_);
+        selection.extend(this.focusNode_, this.focusOffset_);
+        return selection;
+      }
+      if (this.focusNode_) {
+        selection.collapse(this.focusNode_, this.focusOffset_);
+        return selection;
+      }
+      throw new Error('There is no focus marker');
+    }
+
+    /**
+     * @private
+     * @param {!CharacterData} node
+     * @param {number} nodeIndex
+     */
+    handleCharacterData(node, nodeIndex) {
+      /** @type {string} */
+      const text = node.nodeValue;
+      /** @type {number} */
+      const anchorOffset = text.indexOf('^');
+      /** @type {number} */
+      const focusOffset = text.indexOf('|');
+      /** @type {!Node} */
+      const parentNode = node.parentNode;
+      node.nodeValue = text.replace('^', '').replace('|', '');
+      if (node.nodeValue.length == 0) {
+        if (anchorOffset >= 0)
+          this.rememberSelectionAnchor(parentNode, nodeIndex);
+        if (focusOffset >= 0)
+          this.rememberSelectionFocus(parentNode, nodeIndex);
+        node.remove();
+        return;
+      }
+      if (anchorOffset >= 0 && focusOffset >= 0) {
+        if (anchorOffset > focusOffset) {
+          this.rememberSelectionAnchor(node, anchorOffset - 1);
+          this.rememberSelectionFocus(node, focusOffset);
+          return;
+        }
+        this.rememberSelectionAnchor(node, anchorOffset);
+        this.rememberSelectionFocus(node, focusOffset - 1);
+        return;
+      }
+      if (anchorOffset >= 0) {
+        this.rememberSelectionAnchor(node, anchorOffset);
+        return;
+      }
+      if (focusOffset < 0)
+        return;
+      this.rememberSelectionFocus(node, focusOffset);
+    }
+
+    /**
+     * @private
+     * @param {!Element} element
+     */
+    handleElementNode(element) {
+      /** @type {number} */
+      let childIndex = 0;
+      for (const child of Array.from(element.childNodes)) {
+        this.parseInternal(child, childIndex);
+        if (!child.parentNode)
+          continue;
+        ++childIndex;
+      }
+    }
+
+    /**
+   * @private
+   * @param {!Node} node
+   * @return {!SampleSelection}
+   */
+    parse(node) {
+      this.parseInternal(node, 0);
+      return this.selection;
+    }
+
+    /**
+     * @private
+     * @param {!Node} node
+     * @param {number} nodeIndex
+     */
+    parseInternal(node, nodeIndex) {
+      if (isElement(node))
+        return this.handleElementNode(node);
+      if (isCharacterData(node))
+        return this.handleCharacterData(node, nodeIndex);
+      throw new Error(`Unexpected node ${node}`);
+    }
+
+    /**
+     * @private
+     * @param {!Node} node
+     * @param {number} offset
+     */
+    rememberSelectionAnchor(node, offset) {
+      checkValidNodeAndOffset(node, offset);
+      console.assert(
+          this.anchorNode_ === null, 'Anchor marker should be one.',
+          this.anchorNode_, this.anchorOffset_);
+      this.anchorNode_ = node;
+      this.anchorOffset_ = offset;
+    }
+
+    /**
+     * @private
+     * @param {!Node} node
+     * @param {number} offset
+     */
+    rememberSelectionFocus(node, offset) {
+      checkValidNodeAndOffset(node, offset);
+      console.assert(
+          this.focusNode_ === null, 'Focus marker should be one.',
+          this.focusNode_, this.focusOffset_);
+      this.focusNode_ = node;
+      this.focusOffset_ = offset;
+    }
+
+    /**
+   * @public
+   * @param {!Node} node
+   * @return {!SampleSelection}
+   */
+    static parse(node) { return (new Parser()).parse(node); }
+  }
+
+  // TODO(yosin): Once we can import JavaScript file from scripts, we should
+  // import "imported/wpt/html/resources/common.js", since |HTML5_VOID_ELEMENTS|
+  // is defined in there.
+  /**
+   * @const @type {!Set<string>}
+   * only void (without end tag) HTML5 elements
+   */
+  const HTML5_VOID_ELEMENTS = new Set([
+    'area', 'base', 'br', 'col', 'command', 'embed', 'hr', 'img', 'input',
+    'keygen', 'link', 'meta', 'param', 'source', 'track', 'wbr'
+  ]);
+
+  class Serializer {
+    /**
+     * @public
+     * @param {!SampleSelection} selection
+     * @param {!Traversal} traversal
+     */
+    constructor(selection, traversal) {
+      /** @type {!SampleSelection} */
+      this.selection_ = selection;
+      /** @type {!Array<strings>} */
+      this.strings_ = [];
+      /** @type {!Traversal} */
+      this.traversal_ = traversal;
+    }
+
+    /**
+     * @private
+     * @param {string} string
+     */
+    emit(string) { this.strings_.push(string); }
+
+    /**
+     * @private
+     * @param {!HTMLElement} parentNode
+     * @param {number} childIndex
+     */
+    handleSelection(parentNode, childIndex) {
+      if (this.selection_.isNone)
+        return;
+      if (this.selection_.shadowHost)
+        return;
+      if (parentNode === this.selection_.focusNode &&
+          childIndex === this.selection_.focusOffset) {
+        this.emit('|');
+        return;
+      }
+      if (parentNode === this.selection_.anchorNode &&
+          childIndex === this.selection_.anchorOffset) {
+        this.emit('^');
+      }
+    }
+
+    /**
+     * @private
+     * @param {!CharacterData} node
+     */
+    handleCharacterData(node) {
+      /** @type {string} */
+      const text = node.nodeValue;
+      if (this.selection_.isNone)
+        return this.emit(text);
+      /** @type {number} */
+      const anchorOffset = this.selection_.anchorOffset;
+      /** @type {number} */
+      const focusOffset = this.selection_.focusOffset;
+      if (node === this.selection_.focusNode &&
+          node === this.selection_.anchorNode) {
+        if (anchorOffset === focusOffset) {
+          this.emit(text.substr(0, focusOffset));
+          this.emit('|');
+          this.emit(text.substr(focusOffset));
+          return;
+        }
+        if (anchorOffset < focusOffset) {
+          this.emit(text.substr(0, anchorOffset));
+          this.emit('^');
+          this.emit(text.substr(anchorOffset, focusOffset - anchorOffset));
+          this.emit('|');
+          this.emit(text.substr(focusOffset));
+          return;
+        }
+        this.emit(text.substr(0, focusOffset));
+        this.emit('|');
+        this.emit(text.substr(focusOffset, anchorOffset - focusOffset));
+        this.emit('^');
+        this.emit(text.substr(anchorOffset));
+        return;
+      }
+      if (node === this.selection_.anchorNode) {
+        this.emit(text.substr(0, anchorOffset));
+        this.emit('^');
+        this.emit(text.substr(anchorOffset));
+        return;
+      }
+      if (node === this.selection_.focusNode) {
+        this.emit(text.substr(0, focusOffset));
+        this.emit('|');
+        this.emit(text.substr(focusOffset));
+        return;
+      }
+      this.emit(text);
+    }
+
+    /**
+     * @private
+     * @param {!HTMLElement} element
+     */
+    handleElementNode(element) {
+      /** @type {string} */
+      const tagName = element.tagName.toLowerCase();
+      this.emit(`<${tagName}`);
+      Array.from(element.attributes)
+          .sort((attr1, attr2) => attr1.name.localeCompare(attr2.name))
+          .forEach(attr => {
+            if (attr.value === '')
+              return this.emit(` ${attr.name}`);
+            const value = attr.value.replace(/&/g, '&amp;')
+                              .replace(/\u0022/g, '&quot;')
+                              .replace(/\u0027/g, '&apos;');
+            this.emit(` ${attr.name}="${value}"`);
+          });
+      this.emit('>');
+      if (element.nodeName === kTextArea)
+        return this.handleTextArea(element);
+      if (this.traversal_.firstChildOf(element) === null &&
+          HTML5_VOID_ELEMENTS.has(tagName)) {
+        return;
+      }
+      this.serializeChildren(element);
+      this.emit(`</${tagName}>`);
+    }
+
+    /**
+     * @private
+     * @param {!HTMLTextArea}
+     */
+    handleTextArea(textArea) {
+      /** @type {string} */
+      const value = textArea.value;
+      if (this.selection_.shadowHost !== textArea) {
+        this.emit(value);
+      } else {
+        /** @type {number} */
+        const start = textArea.selectionStart;
+        /** @type {number} */
+        const end = textArea.selectionEnd;
+        /** @type {boolean} */
+        const isBackward =
+            start < end && textArea.selectionDirection === 'backward';
+        const startMarker = isBackward ? '|' : '^';
+        const endMarker = isBackward ? '^' : '|';
+        this.emit(value.substr(0, start));
+        if (start < end) {
+          this.emit(startMarker);
+          this.emit(value.substr(start, end - start));
+        }
+        this.emit(endMarker);
+        this.emit(value.substr(end));
+      }
+      this.emit('</textarea>');
+    }
+
+    /**
+     * @public
+     * @param {!HTMLDocument} document
+     */
+    serialize(document) {
+      if (document.body)
+        this.serializeChildren(document.body);
+      else
+        this.serializeInternal(document.documentElement);
+      return this.strings_.join('');
+    }
+
+    /**
+     * @private
+     * @param {!HTMLElement} element
+     */
+    serializeChildren(element) {
+      if (this.traversal_.firstChildOf(element) === null) {
+        this.handleSelection(element, 0);
+        return;
+      }
+
+      /** @type {number} */
+      let childIndex = 0;
+      for (let child of this.traversal_.childNodesOf(element)) {
+        this.handleSelection(element, childIndex);
+        this.serializeInternal(child, childIndex);
+        ++childIndex;
+      }
+      this.handleSelection(element, childIndex);
+    }
+
+    /**
+     * @private
+     * @param {!Node} node
+     */
+    serializeInternal(node) {
+      if (isElement(node))
+        return this.handleElementNode(node);
+      if (isCharacterData(node))
+        return this.handleCharacterData(node);
+      throw new Error(`Unexpected node ${node}`);
+    }
+  }
+
+  /**
+   * @this {!DOMSelection}
+   * @param {string} html
+   * @param {string=} opt_text
+   */
+  function setClipboardData(html, opt_text) {
+    assert_not_equals(
+        window.internals, undefined,
+        'This test requests clipboard access from JavaScript.');
+    function computeTextData() {
+      if (opt_text !== undefined)
+        return opt_text;
+      const element = document.createElement('div');
+      element.innerHTML = html;
+      return element.textContent;
+    }
+    function copyHandler(event) {
+      const clipboardData = event.clipboardData;
+      clipboardData.setData('text/plain', computeTextData());
+      clipboardData.setData('text/html', html);
+      event.preventDefault();
+    }
+    document.addEventListener('copy', copyHandler);
+    document.execCommand('copy');
+    document.removeEventListener('copy', copyHandler);
+  }
+
+  class Sample {
+    /**
+     * @public
+     * @param {string} sampleText
+     */
+    constructor(sampleText) {
+      /** @const @type {!HTMLIFame} */
+      this.iframe_ = document.createElement('iframe');
+      if (!document.body)
+        document.body = document.createElement('body');
+      document.body.appendChild(this.iframe_);
+      /** @const @type {!HTMLDocument} */
+      this.document_ = this.iframe_.contentDocument;
+      /** @const @type {!Selection} */
+      this.selection_ = this.iframe_.contentWindow.getSelection();
+      this.selection_.document = this.document_;
+      this.selection_.document.offsetLeft = this.iframe_.offsetLeft;
+      this.selection_.document.offsetTop = this.iframe_.offsetTop;
+      this.selection_.setClipboardData = setClipboardData;
+
+      // Set focus to sample IFRAME to make |eventSender| and
+      // |testRunner.execCommand()| to work on sample rather than main frame.
+      this.iframe_.focus();
+      this.load(sampleText);
+    }
+
+    /** @return {!HTMLDocument} */
+    get document() { return this.document_; }
+
+    /** @return {!Selection} */
+    get selection() { return this.selection_; }
+
+    /**
+     * @private
+     * @param {string} sampleText
+     */
+    load(sampleText) {
+      const anchorMarker = sampleText.indexOf('^');
+      const focusMarker = sampleText.indexOf('|');
+      if (focusMarker < 0 && anchorMarker >= 0) {
+        throw new Error(
+            `You should specify caret position in "${sampleText}".`);
+      }
+      if (focusMarker != sampleText.lastIndexOf('|')) {
+        throw new Error(
+            `You should have at least one focus marker "|" in "${sampleText
+            }".`);
+      }
+      if (anchorMarker != sampleText.lastIndexOf('^')) {
+        throw new Error(
+            `You should have at most one anchor marker "^" in "${sampleText
+            }".`);
+      }
+      if (anchorMarker >= 0 && focusMarker >= 0 &&
+          (anchorMarker + 1 === focusMarker ||
+           anchorMarker - 1 === focusMarker)) {
+        throw new Error(
+            `You should have focus marker and should not have anchor marker if and only if selection is a caret in "${sampleText
+            }".`);
+      }
+      this.document_.body.innerHTML = sampleText;
+      /** @type {!SampleSelection} */
+      const selection = Parser.parse(this.document_.body);
+      if (selection.isNone)
+        return;
+      if (this.loadSelectionInTextArea(selection))
+        return;
+      this.selection_.collapse(selection.anchorNode, selection.anchorOffset);
+      this.selection_.extend(selection.focusNode, selection.focusOffset);
+    }
+
+    /**
+   * @private
+   * @param {!SampleSelection} selection
+   * @return {boolean} Returns true if selection is in TEXTAREA.
+   */
+    loadSelectionInTextArea(selection) {
+      /** @type {Node} */
+      const enclosingNode = selection.anchorNode.parentNode;
+      if (selection.focusNode.parentNode !== enclosingNode)
+        return false;
+      if (enclosingNode.nodeName !== kTextArea)
+        return false;
+      if (selection.anchorNode !== selection.focusNode)
+        throw new Error('Selection in TEXTAREA should be in same Text node.');
+      enclosingNode.focus();
+      if (selection.anchorOffset < selection.focusOffset) {
+        enclosingNode.setSelectionRange(
+            selection.anchorOffset, selection.focusOffset);
+        return true;
+      }
+      enclosingNode.setSelectionRange(
+          selection.focusOffset, selection.anchorOffset, 'backward');
+      return true;
+    }
+
+    /**
+     * @public
+     */
+    remove() { this.iframe_.remove(); }
+
+    /**
+   * @public
+   * @param {!Traversal} traversal
+   * @return {string}
+   */
+    serialize(traversal) {
+      /** @type {!SampleSelection} */
+      const selection = traversal.fromDOMSelection(this.selection_);
+      /** @type {!Serializer} */
+      const serializer = new Serializer(selection, traversal);
+      return serializer.serialize(this.document_);
+    }
+  }
+
+  function assembleDescription() {
+    function getStack() {
+      let stack;
+      try {
+        throw new Error('get line number');
+      } catch (error) {
+        stack = error.stack.split('\n').slice(1);
+      }
+      return stack
+    }
+
+    const RE_IN_ASSERT_SELECTION = new RegExp('assert_selection\\.js');
+    for (const line of getStack()) {
+      const match = RE_IN_ASSERT_SELECTION.exec(line);
+      if (!match) {
+        const RE_LAYOUTTESTS = new RegExp('LayoutTests.*');
+        return RE_LAYOUTTESTS.exec(line);
+      }
+    }
+    return '';
+  }
+
+  /**
+   * @param {string} expectedText
+   */
+  function checkExpectedText(expectedText) {
+    /** @type {number} */
+    const anchorOffset = expectedText.indexOf('^');
+    /** @type {number} */
+    const focusOffset = expectedText.indexOf('|');
+    if (anchorOffset != expectedText.lastIndexOf('^')) {
+      throw new Error(
+          `You should have at most one anchor marker "^" in "${expectedText
+          }".`);
+    }
+    if (focusOffset != expectedText.lastIndexOf('|')) {
+      throw new Error(
+          `You should have at most one focus marker "|" in "${expectedText}".`);
+    }
+    if (anchorOffset >= 0 && focusOffset < 0) {
+      throw new Error(
+          `You should have a focus marker "|" in "${expectedText}".`);
+    }
+    if (anchorOffset >= 0 && focusOffset >= 0 &&
+        (anchorOffset + 1 === focusOffset ||
+         anchorOffset - 1 === focusOffset)) {
+      throw new Error(
+          `You should have focus marker and should not have anchor marker if and only if selection is a caret in "${expectedText
+          }".`);
+    }
+  }
+
+  /**
+ * @param {string} str1
+ * @param {string} str2
+ * @return {string}
+ */
+  function commonPrefixOf(str1, str2) {
+    for (let index = 0; index < str1.length; ++index) {
+      if (str1[index] !== str2[index])
+        return str1.substr(0, index);
+    }
+    return str1;
+  }
+
+  /**
+ * @param {string} inputText
+ * @param {function(!Selection)|string}
+ * @param {string} expectedText
+ * @param {Object=} opt_options
+ * @return {!Sample}
+ */
+  function assertSelection(inputText, tester, expectedText, opt_options = {}) {
+    const kDescription = 'description';
+    const kDumpAs = 'dumpAs';
+    const kRemoveSampleIfSucceeded = 'removeSampleIfSucceeded';
+    /** @type {!Object} */
+    const options = typeof(opt_options) === 'string' ?
+        {description: opt_options} :
+        opt_options;
+    /** @type {string} */
+    const description =
+        kDescription in options ? options[kDescription] : assembleDescription();
+    /** @type {boolean} */
+    const removeSampleIfSucceeded = kRemoveSampleIfSucceeded in options ?
+        !!options[kRemoveSampleIfSucceeded] :
+        true;
+    /** @type {DumpAs} */
+    const dumpAs = options[kDumpAs] || DumpAs.DOM_TREE;
+
+    checkExpectedText(expectedText);
+    const sample = new Sample(inputText);
+    if (typeof(tester) === 'function') {
+      tester.call(window, sample.selection);
+    } else if (typeof(tester) === 'string') {
+      const strings = tester.split(/ (.+)/);
+      sample.document.execCommand(strings[0], false, strings[1]);
+    } else {
+      throw new Error(`Invalid tester: ${tester}`);
+    }
+
+    /** @type {!Traversal} */
+    const traversal = (() => {
+      switch (dumpAs) {
+        case DumpAs.DOM_TREE:
+          return new DOMTreeTraversal();
+        case DumpAs.FLAT_TREE:
+          if (!window.internals)
+            throw new Error('This test requires window.internals.');
+          return new FlatTreeTraversal();
+        default:
+          throw `${kDumpAs} must be one of ` +
+              `{${Object.values(DumpAs).join(', ')}}` +
+              ` instead of '${dumpAs}'`;
+      }
+    })();
+
+    /** @type {string} */
+    const actualText = sample.serialize(traversal);
+    // We keep sample HTML when assertion is false for ease of debugging test
+    // case.
+    if (actualText === expectedText) {
+      if (removeSampleIfSucceeded)
+        sample.remove();
+      return sample;
+    }
+    throw new Error(
+        `${description}\n` +
+        `\t expected ${expectedText},\n` +
+        `\t but got  ${actualText},\n` +
+        `\t sameupto ${commonPrefixOf(expectedText, actualText)}`);
+  }
+
+  // Export symbols
+  window.Sample = Sample;
+  window.assert_selection = assertSelection;
+})();