anchor.diff:        for(int y = 0; y < f.rows; y++) {
           final i = x + y * f.cols;
           final adj = f.getAdjacent(x, y);
  -        expect(adj, equals(source[i]));
  +        expect(adj, equals(sample[i]));
         }
       }
     }
  
positive.code:   }
  
    static void _testAdjacent() {
      // This grid
      // XXXXX2
      // X7X8X3
      // X5XXX2
      // X32321
      // 110000
  
      final source = [null, null, null, null, null, 2,
                      null,    7, null,    8, null, 3,
                      null,    5, null, null, null, 2,
                      null,    3,    2,    3,    2, 1,
                         1,    1,    0,    0,    0, 0];
  
      final bools = new List<bool>.from(source.map((x) => x == null));
  
      final f = new Field.fromSquares(6, 5, bools);
  
      expect(f.mineCount, equals(13));
  
  
negative.code: class FieldTest {
    // This grid
    // XXXXX2
    // X7X8X3
    // X5XXX2
    // X32321
    // 110000
  
    static final sample = const
        [null, null, null, null, null, 2,
         null,    7, null,    8, null, 3,
         null,    5, null, null, null, 2,
         null,    3,    2,    3,    2, 1,
            1,    1,    0,    0,    0, 0];
  
  
    static Field getSampleField() {
      final bools = new List<bool>.from(sample.map((x) => x == null));
  
      return new Field.fromSquares(6, 5, bools);
    }
  
    static void run() {
      test('defaults', _testDefaults);
      test('mineCount', _testMineCount);
  