go.image/bmp: add a test image for top-down BMPs.

LGTM=ruiu
R=ruiu
CC=bsiegert, golang-codereviews
https://golang.org/cl/149090043

bmp/reader_test.go

@@ -5,6 +5,7 @@
 package bmp
 
 import (
+	"fmt"
 	"image"
 	"os"
 	"testing"
@@ -14,10 +15,10 @@ import (
 
 const testdataDir = "../testdata/"
 
-func compare(t *testing.T, img0, img1 image.Image) {
+func compare(t *testing.T, img0, img1 image.Image) error {
 	b := img1.Bounds()
 	if !b.Eq(img0.Bounds()) {
-		t.Fatalf("wrong image size: want %s, got %s", img0.Bounds(), b)
+		return fmt.Errorf("wrong image size: want %s, got %s", img0.Bounds(), b)
 	}
 	for y := b.Min.Y; y < b.Max.Y; y++ {
 		for x := b.Min.X; x < b.Max.X; x++ {
@@ -26,34 +27,49 @@ func compare(t *testing.T, img0, img1 image.Image) {
 			r0, g0, b0, a0 := c0.RGBA()
 			r1, g1, b1, a1 := c1.RGBA()
 			if r0 != r1 || g0 != g1 || b0 != b1 || a0 != a1 {
-				t.Fatalf("pixel at (%d, %d) has wrong color: want %v, got %v", x, y, c0, c1)
+				return fmt.Errorf("pixel at (%d, %d) has wrong color: want %v, got %v", x, y, c0, c1)
 			}
 		}
 	}
+	return nil
 }
 
 // TestDecode tests that decoding a PNG image and a BMP image result in the
 // same pixel data.
 func TestDecode(t *testing.T) {
-	f0, err := os.Open(testdataDir + "video-001.png")
+	testCases := []string{
+		"video-001",
+		"yellow_rose-small",
+	}
+
+	for _, tc := range testCases {
+		f0, err := os.Open(testdataDir + tc + ".png")
 		if err != nil {
-		t.Fatal(err)
+			t.Errorf("%s: Open PNG: %v", tc, err)
+			continue
 		}
 		defer f0.Close()
 		img0, _, err := image.Decode(f0)
 		if err != nil {
-		t.Fatal(err)
+			t.Errorf("%s: Decode PNG: %v", tc, err)
+			continue
 		}
 
-	f1, err := os.Open(testdataDir + "video-001.bmp")
+		f1, err := os.Open(testdataDir + tc + ".bmp")
 		if err != nil {
-		t.Fatal(err)
+			t.Errorf("%s: Open BMP: %v", tc, err)
+			continue
 		}
 		defer f1.Close()
 		img1, _, err := image.Decode(f1)
 		if err != nil {
-		t.Fatal(err)
+			t.Errorf("%s: Decode BMP: %v", tc, err)
+			continue
 		}
 
-	compare(t, img0, img1)
+		if err := compare(t, img0, img1); err != nil {
+			t.Errorf("%s: %v", tc, err)
+			continue
+		}
+	}
 }