anchor.diff:           0.5, -0.5,     0.0, 0.0, 1.0
         ]);
   
  -      var vertices = new VertexArray.fromAttributes({
  +      var vertices = new VertexArray.fromAttributes(<String, VertexAttribute>{
           'position': new Vector2Attribute(attributeData),
           'color': new Vector3Attribute(attributeData, offset: 2)
         });
  
positive.code: 
        group('indexOf', () {
          test('returns -1 if the vertex is not in the vertex array', () {
            final other = new VertexArray.fromAttributes({
              'position': new Vector2Attribute(attributeData),
              'color': new Vector3Attribute(attributeData, offset: 2)
            });
  
negative.code:         0.0, 1.0, 0.0,
          0.0, 0.0, 1.0
        ]);
        final vertices = new VertexArray.fromAttributes(<String, VertexAttribute>{
          'position': new Vector2Attribute(positionData),
          'color': new Vector3Attribute(colorData)
        });
  