anchor.diff:     * given tolerance. If no tolerance is given, tolerance is assumed to be the
      * value 4 significant digits smaller than the value given for expected.
      */
  -  @deprecated
     static void approxEquals(num expected,
                              num actual,
                              [num tolerance = null,
  
positive.code: 
  typedef bool _CheckExceptionFn(exception);
  
  @deprecated
  class ExpectException implements Exception {
    ExpectException(this.message);
    String toString() => message;
  
negative.code:   }
  
    // Unconditional failure.
    static void fail(String msg) {
      _fail("Expect.fail('$msg')");
    }
  