Cleanup tests (#656)

I've replaced a few tests with synthetic images and removed a number
that I don't believe are relevant anymore.

I've also removed the #553 test without replacement as I don't know how
to synthesise a replacement and the issue is still open anyway.

Going forward I think we should avoid adding any new "issue" tests and
instead synthesise something suitable in one of the other collections.

Closes #655.

tests/flags.rs

@@ -12,10 +12,8 @@ use std::{
 use indexmap::indexset;
 use oxipng::{internal_tests::*, *};
 
-const GRAYSCALE: u8 = 0;
 const RGB: u8 = 2;
 const INDEXED: u8 = 3;
-const RGBA: u8 = 6;
 
 fn get_opts(input: &Path) -> (OutFile, oxipng::Options) {
     let mut options = oxipng::Options {
@@ -582,7 +580,7 @@ fn fix_errors() {
 
     let png = PngData::new(&input, &opts).unwrap();
 
-    assert_eq!(png.raw.ihdr.color_type.png_header_code(), RGBA);
+    assert_eq!(png.raw.ihdr.color_type.png_header_code(), INDEXED);
     assert_eq!(png.raw.ihdr.bit_depth, BitDepth::Eight);
 
     match oxipng::optimize(&InFile::Path(input), &output, &opts) {
@@ -600,7 +598,7 @@ fn fix_errors() {
         }
     };
 
-    assert_eq!(png.raw.ihdr.color_type.png_header_code(), GRAYSCALE);
+    assert_eq!(png.raw.ihdr.color_type.png_header_code(), INDEXED);
     assert_eq!(png.raw.ihdr.bit_depth, BitDepth::Eight);
 
     // Cannot check if pixels are equal because image crate cannot read corrupt (input) PNGs
@@ -688,9 +686,9 @@ fn zopfli_mode() {
         input,
         &output,
         &opts,
-        INDEXED,
+        RGB,
         BitDepth::Eight,
-        INDEXED,
+        RGB,
         BitDepth::Eight,
     );
 }

tests/interlaced.rs

@@ -666,6 +666,17 @@ fn interlaced_small_files() {
     );
 }
 
+#[test]
+fn interlaced_vertical_filters() {
+    test_it_converts(
+        "tests/files/interlaced_vertical_filters.png",
+        RGB,
+        BitDepth::Eight,
+        RGB,
+        BitDepth::Eight,
+    );
+}
+
 #[test]
 fn interlaced_odd_width() {
     test_it_converts(

tests/reduction.rs

@@ -386,6 +386,18 @@ fn rgb_8_should_be_palette_8() {
     );
 }
 
+#[test]
+fn rgb_trns_8_should_be_palette_8() {
+    test_it_converts(
+        "tests/files/rgb_trns_8_should_be_palette_8.png",
+        false,
+        RGB,
+        BitDepth::Eight,
+        INDEXED,
+        BitDepth::Eight,
+    );
+}
+
 #[test]
 fn rgb_16_should_be_palette_4() {
     test_it_converts(
@@ -722,6 +734,18 @@ fn grayscale_alpha_8_should_be_grayscale_8() {
     );
 }
 
+#[test]
+fn grayscale_alpha_8_should_be_palette_8() {
+    test_it_converts(
+        "tests/files/grayscale_alpha_8_should_be_palette_8.png",
+        false,
+        GRAYSCALE_ALPHA,
+        BitDepth::Eight,
+        INDEXED,
+        BitDepth::Eight,
+    );
+}
+
 #[test]
 fn grayscale_16_should_be_grayscale_16() {
     test_it_converts(
@@ -926,6 +950,18 @@ fn grayscale_alpha_8_should_be_grayscale_trns_1() {
     );
 }
 
+#[test]
+fn grayscale_trns_8_should_be_grayscale_1() {
+    test_it_converts(
+        "tests/files/grayscale_trns_8_should_be_grayscale_1.png",
+        true,
+        GRAYSCALE,
+        BitDepth::Eight,
+        GRAYSCALE,
+        BitDepth::One,
+    );
+}
+
 #[test]
 fn small_files() {
     test_it_converts(
@@ -1012,6 +1048,45 @@ fn palette_should_be_reduced_with_unused() {
     remove_file(output).ok();
 }
 
+#[test]
+fn palette_should_be_reduced_with_bkgd() {
+    let input = PathBuf::from("tests/files/palette_should_be_reduced_with_bkgd.png");
+    let (output, opts) = get_opts(&input);
+
+    let png = PngData::new(&input, &opts).unwrap();
+
+    assert_eq!(png.raw.ihdr.color_type.png_header_code(), INDEXED);
+    assert_eq!(png.raw.ihdr.bit_depth, BitDepth::One);
+    assert_eq!(&png.aux_chunks[0].name, b"bKGD");
+    if let ColorType::Indexed { palette } = &png.raw.ihdr.color_type {
+        assert_eq!(palette.len(), 3);
+    }
+
+    match oxipng::optimize(&InFile::Path(input), &output, &opts) {
+        Ok(_) => (),
+        Err(x) => panic!("{}", x),
+    };
+    let output = output.path().unwrap();
+    assert!(output.exists());
+
+    let png = match PngData::new(output, &opts) {
+        Ok(x) => x,
+        Err(x) => {
+            remove_file(output).ok();
+            panic!("{}", x)
+        }
+    };
+
+    assert_eq!(png.raw.ihdr.color_type.png_header_code(), INDEXED);
+    assert_eq!(png.raw.ihdr.bit_depth, BitDepth::One);
+    assert_ne!(&png.aux_chunks[0].name, b"bKGD");
+    if let ColorType::Indexed { palette } = &png.raw.ihdr.color_type {
+        assert_eq!(palette.len(), 2);
+    }
+
+    remove_file(output).ok();
+}
+
 #[test]
 fn palette_should_be_reduced_with_both() {
     let input = PathBuf::from("tests/files/palette_should_be_reduced_with_both.png");