1 files changed, 110 insertions, 2 deletions
diff --git a/libgo/go/image/png/writer_test.go b/libgo/go/image/png/writer_test.go
index 1107ea0e7fc..5d131ff823a 100644
--- a/libgo/go/image/png/writer_test.go
+++ b/libgo/go/image/png/writer_test.go
@@ -6,9 +6,12 @@ package png
 
 import (
 	"bytes"
+	"compress/zlib"
+	"encoding/binary"
 	"fmt"
 	"image"
 	"image/color"
+	"io"
 	"io/ioutil"
 	"testing"
 )
@@ -61,12 +64,12 @@ func TestWriter(t *testing.T) {
 		m1, err := readPNG(qfn)
 		if err != nil {
 			t.Error(fn, err)
-			return
+			continue
 		}
 		m2, err := encodeDecode(m1)
 		if err != nil {
 			t.Error(fn, err)
-			return
+			continue
 		}
 		// Compare the two.
 		err = diff(m0, m2)
@@ -77,6 +80,111 @@ func TestWriter(t *testing.T) {
 	}
 }
 
+func TestWriterPaletted(t *testing.T) {
+	const width, height = 32, 16
+
+	testCases := []struct {
+		plen     int
+		bitdepth uint8
+		datalen  int
+	}{
+
+		{
+			plen:     256,
+			bitdepth: 8,
+			datalen:  (1 + width) * height,
+		},
+
+		{
+			plen:     128,
+			bitdepth: 8,
+			datalen:  (1 + width) * height,
+		},
+
+		{
+			plen:     16,
+			bitdepth: 4,
+			datalen:  (1 + width/2) * height,
+		},
+
+		{
+			plen:     4,
+			bitdepth: 2,
+			datalen:  (1 + width/4) * height,
+		},
+
+		{
+			plen:     2,
+			bitdepth: 1,
+			datalen:  (1 + width/8) * height,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(fmt.Sprintf("plen-%d", tc.plen), func(t *testing.T) {
+			// Create a paletted image with the correct palette length
+			palette := make(color.Palette, tc.plen)
+			for i := range palette {
+				palette[i] = color.NRGBA{
+					R: uint8(i),
+					G: uint8(i),
+					B: uint8(i),
+					A: 255,
+				}
+			}
+			m0 := image.NewPaletted(image.Rect(0, 0, width, height), palette)
+
+			i := 0
+			for y := 0; y < height; y++ {
+				for x := 0; x < width; x++ {
+					m0.SetColorIndex(x, y, uint8(i%tc.plen))
+					i++
+				}
+			}
+
+			// Encode the image
+			var b bytes.Buffer
+			if err := Encode(&b, m0); err != nil {
+				t.Error(err)
+				return
+			}
+			const chunkFieldsLength = 12 // 4 bytes for length, name and crc
+			data := b.Bytes()
+			i = len(pngHeader)
+
+			for i < len(data)-chunkFieldsLength {
+				length := binary.BigEndian.Uint32(data[i : i+4])
+				name := string(data[i+4 : i+8])
+
+				switch name {
+				case "IHDR":
+					bitdepth := data[i+8+8]
+					if bitdepth != tc.bitdepth {
+						t.Errorf("got bitdepth %d, want %d", bitdepth, tc.bitdepth)
+					}
+				case "IDAT":
+					// Uncompress the image data
+					r, err := zlib.NewReader(bytes.NewReader(data[i+8 : i+8+int(length)]))
+					if err != nil {
+						t.Error(err)
+						return
+					}
+					n, err := io.Copy(ioutil.Discard, r)
+					if err != nil {
+						t.Errorf("got error while reading image data: %v", err)
+					}
+					if n != int64(tc.datalen) {
+						t.Errorf("got uncompressed data length %d, want %d", n, tc.datalen)
+					}
+				}
+
+				i += chunkFieldsLength + int(length)
+			}
+		})
+
+	}
+}
+
 func TestWriterLevels(t *testing.T) {
 	m := image.NewNRGBA(image.Rect(0, 0, 100, 100))