message: Add conversion test
diff: @@ -966,4 +966,12 @@ mod tests {
  test_lossless_conversion!(Rgb<u8>, Rgb<u16>, Rgb<u8>);
  test_lossless_conversion!(Rgba<u8>, Rgba<u16>, Rgba<u8>);
  }
  +
  + #[test]
  + fn accuracy_conversion() {
  + use super::{Luma, Pixel, Rgb};
  + let pixel = Rgb::from([13, 13, 13]);
  + let Luma([luma]) = pixel.to_luma();
  + assert_eq!(luma, 13);
  + }
  }
  