anchor.diff:      }
       return object;
     }
  -
  -  /**
  -   * Assert that the actual token has the same type and lexeme as the expected token. Note that this
  -   * does not assert anything about the offsets of the tokens (although the lengths will be equal).
  -   *
  -   * @param expectedToken the token that was expected
  -   * @param actualToken the token that was found
  -   * @throws AssertionFailedError if the two tokens are not the same
  -   */
  -  static void assertMatches(Token expectedToken, Token actualToken) {
  -    expect(actualToken.type, expectedToken.type);
  -    if (expectedToken is KeywordToken) {
  -      assertInstanceOf((obj) => obj is KeywordToken, KeywordToken, actualToken);
  -      expect((actualToken as KeywordToken).keyword, expectedToken.keyword);
  -    } else if (expectedToken is StringToken) {
  -      assertInstanceOf((obj) => obj is StringToken, StringToken, actualToken);
  -      expect((actualToken as StringToken).lexeme, expectedToken.lexeme);
  -    }
  -  }
  -
   
     /**
      * @return the [AstNode] with requested type at offset of the "prefix".
  
positive.code:     }
      AstNode node = new NodeLocator.con1(offset).searchWithin(root);
      return node.getAncestor(predicate);
    }
  
    /**
     * Calculate the offset where the given strings differ.
     *
     * @param str1 the first String to compare
     * @param str2 the second String to compare
     * @return the offset at which the strings differ (or <code>-1</code> if they do not)
     */
    static int _getDiffPos(String str1, String str2) {
      int len1 = math.min(str1.length, str2.length);
      int diffPos = -1;
      for (int i = 0; i < len1; i++) {
        if (str1.codeUnitAt(i) != str2.codeUnitAt(i)) {
          diffPos = i;
          break;
        }
      }
      if (diffPos == -1 && str1.length != str2.length) {
        diffPos = len1;
      }
      return diffPos;
    }
  
    static void _privateAssertContains(List<Object> array, List<bool> found,
  
negative.code:  * The class `EngineTestCase` defines utility methods for making assertions.
   */
  class EngineTestCase {
    void setUp() {}
  
    void tearDown() {}
  