message: Add back mutable_view test
diff: @@ -1418,7 +1418,7 @@ impl PartialOrd for NormalForm {
  mod tests {
  use super::*;
  use buffer::GrayAlphaImage;
  - use color::Rgb;
  + use color::{LumaA, Rgb};
  #[test]
  fn aliasing_view() {
  @@ -1443,6 +1443,35 @@ mod tests {
  assert_eq!(pixel_count, 100*100);
  }
  + #[test]
  + fn mutable_view() {
  + let mut buffer = FlatSamples {
  + samples: [0; 18],
  + layout: SampleLayout {
  + channels: 2,
  + channel_stride: 1,
  + width: 3,
  + width_stride: 2,
  + height: 3,
  + height_stride: 6,
  + },
  + color_hint: None,
  + };
  +
  + {
  + let mut view = buffer.as_view_mut::<LumaA<usize>>()
  + .expect("This should be a valid mutable buffer");
  + assert_eq!(view.dimensions(), (3, 3));
  + for i in 0..9 {
  + *view.get_pixel_mut(i % 3, i / 3) = LumaA([2 * i as usize, 2 * i as usize + 1]);
  + }
  + }
  +
  + buffer.samples.iter()
  + .enumerate()
  + .for_each(|(idx, sample)| assert_eq!(idx, *sample));
  + }
  +
  #[test]
  fn normal_forms() {
  assert!(FlatSamples {
  