test: add unit tests and GitHub Actions CI/CD pipeline

- Added unit tests for core comparison and region ignoring
- Configured GitHub Actions for multi-platform testing (Linux, macOS, Windows)
- Added automatic binary release workflow on tag push

Author: maskedsyntax

.github/workflows/ci.yml

@@ -0,0 +1,54 @@
+name: CI & Release
+
+on:
+  push:
+    branches: [ main ]
+    tags: [ 'v*' ]
+  pull_request:
+    branches: [ main ]
+
+env:
+  CARGO_TERM_COLOR: always
+
+jobs:
+  test:
+    name: Test on ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+
+    steps:
+    - uses: actions/checkout@v4
+    - name: Build
+      run: cargo build --verbose
+    - name: Run tests
+      run: cargo test --verbose
+
+  release:
+    name: Release Binaries
+    if: startsWith(github.ref, 'refs/tags/')
+    needs: test
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        include:
+          - os: ubuntu-latest
+            target: x86_64-unknown-linux-gnu
+            artifact_name: image-diff-linux
+          - os: macos-latest
+            target: x86_64-apple-darwin
+            artifact_name: image-diff-macos
+          - os: windows-latest
+            target: x86_64-pc-windows-msvc
+            artifact_name: image-diff-windows.exe
+
+    steps:
+    - uses: actions/checkout@v4
+    - name: Build release
+      run: cargo build --release --target ${{ matrix.target }}
+    - name: Upload artifact
+      uses: actions/upload-artifact@v4
+      with:
+        name: ${{ matrix.artifact_name }}
+        path: target/${{ matrix.target }}/release/${{ matrix.os == 'windows-latest' && 'image-diff.exe' || 'image-diff' }}

Cargo.toml

@@ -18,3 +18,6 @@ pathdiff = "0.2.1"
 serde = { version = "1.0.200", features = ["derive"] }
 serde_json = "1.0.116"
 image-compare = "0.5.0"
+
+[dev-dependencies]
+tempfile = "3.10.1"

src/compare.rs

@@ -126,3 +126,69 @@ fn color_distance(p1: &Rgba<u8>, p2: &Rgba<u8>) -> f64 {
     // Euclidean distance in RGBA space
     (r_diff * r_diff + g_diff * g_diff + b_diff * b_diff + a_diff * a_diff).sqrt()
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_color_distance() {
+        let p1 = Rgba([0, 0, 0, 255]);
+        let p2 = Rgba([255, 255, 255, 255]);
+        assert!((color_distance(&p1, &p2) - 1.732).abs() < 0.01);
+
+        let p3 = Rgba([100, 100, 100, 255]);
+        assert_eq!(color_distance(&p3, &p3), 0.0);
+    }
+
+    #[test]
+    fn test_region_contains() {
+        let region = Region { x: 10, y: 10, width: 20, height: 20 };
+        assert!(region.contains(10, 10));
+        assert!(region.contains(29, 29));
+        assert!(!region.contains(9, 10));
+        assert!(!region.contains(30, 30));
+    }
+
+    #[test]
+    fn test_compare_identical() -> Result<()> {
+        let mut img: ImageBuffer<Rgba<u8>, Vec<u8>> = ImageBuffer::new(10, 10);
+        for p in img.pixels_mut() { *p = Rgba([100, 100, 100, 255]); }
+        
+        let file_a = tempfile::Builder::new().suffix(".png").tempfile()?;
+        let file_b = tempfile::Builder::new().suffix(".png").tempfile()?;
+        img.save(file_a.path())?;
+        img.save(file_b.path())?;
+
+        let res = compare_images(file_a.path(), file_b.path(), 0.1, false, &[])?;
+        assert_eq!(res.diff_pixels, 0);
+        assert_eq!(res.score, 1.0);
+        assert!(res.ssim_score > 0.99);
+        Ok(())
+    }
+
+    #[test]
+    fn test_compare_different_with_ignore() -> Result<()> {
+        let mut img_a: ImageBuffer<Rgba<u8>, Vec<u8>> = ImageBuffer::new(10, 10);
+        for p in img_a.pixels_mut() { *p = Rgba([100, 100, 100, 255]); }
+        
+        let mut img_b = img_a.clone();
+        img_b.put_pixel(5, 5, Rgba([255, 0, 0, 255]));
+
+        let file_a = tempfile::Builder::new().suffix(".png").tempfile()?;
+        let file_b = tempfile::Builder::new().suffix(".png").tempfile()?;
+        img_a.save(file_a.path())?;
+        img_b.save(file_b.path())?;
+
+        // Without ignore
+        let res1 = compare_images(file_a.path(), file_b.path(), 0.1, false, &[])?;
+        assert_eq!(res1.diff_pixels, 1);
+
+        // With ignore
+        let ignore = [Region { x: 5, y: 5, width: 1, height: 1 }];
+        let res2 = compare_images(file_a.path(), file_b.path(), 0.1, false, &ignore)?;
+        assert_eq!(res2.diff_pixels, 0);
+        assert_eq!(res2.score, 1.0);
+        Ok(())
+    }
+}