anchor.diff:    Expect.equals(1 + 2 + 5 + 10 + 17 + 26 + 37 + 50 + 65 + 82, sum);
   
     // Test Set.filter.
  -  testFilter(int val) {
  -    return val.isEven;
  +  testFilter(Object val) {
  +    return (val as int).isEven;
     }
   
     Set filtered = set.where(testFilter).toSet();
  
positive.code: 
    // Test Set.forEach.
    int sum = 0;
    testForEach(int val) {
      sum += (val + 1);
    }
  
    set.forEach(testForEach);
  
negative.code:   Expect.isFalse(filtered.every(testEvery));
  
    // Test Set.some.
    testSome(Object val) {
      return (val == 4);
    }
  
  