diff --git a/src/pkg/Makefile b/src/pkg/Makefile
index 68e4a16d3a1..2a65d376986 100644
--- a/src/pkg/Makefile
+++ b/src/pkg/Makefile
@@ -121,7 +121,6 @@ DIRS=\
 
 NOTEST=\
 	debug/proc\
-	exp/draw\
 	go/ast\
 	go/doc\
 	go/token\
diff --git a/src/pkg/exp/draw/draw_test.go b/src/pkg/exp/draw/draw_test.go
new file mode 100644
index 00000000000..61794dab885
--- /dev/null
+++ b/src/pkg/exp/draw/draw_test.go
@@ -0,0 +1,89 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package draw
+
+import (
+	"image"
+	"testing"
+)
+
+func eq(c0, c1 image.Color) bool {
+	r0, g0, b0, a0 := c0.RGBA()
+	r1, g1, b1, a1 := c1.RGBA()
+	return r0 == r1 && g0 == g1 && b0 == b1 && a0 == a1
+}
+
+func fillBlue(alpha int) image.Image {
+	return image.ColorImage{image.RGBAColor{0, 0, uint8(alpha), uint8(alpha)}}
+}
+
+func fillAlpha(alpha int) image.Image {
+	return image.ColorImage{image.AlphaColor{uint8(alpha)}}
+}
+
+func vgradGreen(alpha int) image.Image {
+	m := image.NewRGBA(16, 16)
+	for y := 0; y < 16; y++ {
+		for x := 0; x < 16; x++ {
+			m.Set(x, y, image.RGBAColor{0, uint8(y * alpha / 15), 0, uint8(alpha)})
+		}
+	}
+	return m
+}
+
+func vgradAlpha(alpha int) image.Image {
+	m := image.NewAlpha(16, 16)
+	for y := 0; y < 16; y++ {
+		for x := 0; x < 16; x++ {
+			m.Set(x, y, image.AlphaColor{uint8(y * alpha / 15)})
+		}
+	}
+	return m
+}
+
+func hgradRed(alpha int) Image {
+	m := image.NewRGBA(16, 16)
+	for y := 0; y < 16; y++ {
+		for x := 0; x < 16; x++ {
+			m.Set(x, y, image.RGBAColor{uint8(x * alpha / 15), 0, 0, uint8(alpha)})
+		}
+	}
+	return m
+}
+
+type drawTest struct {
+	desc     string
+	src      image.Image
+	mask     image.Image
+	expected image.Color
+}
+
+var drawTests = []drawTest{
+	// Uniform mask (0% opaque) mask.
+	drawTest{"nop", vgradGreen(255), fillAlpha(0), image.RGBAColor{136, 0, 0, 255}},
+	// Uniform mask (100%, 75%, nil) and vertical-gradient source.
+	drawTest{"copy", vgradGreen(90), fillAlpha(255), image.RGBAColor{0, 48, 0, 90}},
+	drawTest{"copyAlpha", vgradGreen(90), fillAlpha(192), image.RGBAColor{100, 36, 0, 255}},
+	drawTest{"copyNil", vgradGreen(90), nil, image.RGBAColor{0, 48, 0, 90}},
+	// Uniform mask (100%, 75%, nil) and uniform source.
+	drawTest{"fill", fillBlue(90), fillAlpha(255), image.RGBAColor{0, 0, 90, 90}},
+	drawTest{"fillAlpha", fillBlue(90), fillAlpha(192), image.RGBAColor{100, 0, 68, 255}},
+	drawTest{"fillNil", fillBlue(90), nil, image.RGBAColor{0, 0, 90, 90}},
+	// Variable mask. In detail, at (x, y) == (8, 8):
+	// The destination pixel is {136, 0, 0, 255}.
+	// The source pixel is {0, 0, 255, 255}.
+	// The mask pixel's alpha is 102, or 40%.
+	drawTest{"generic", fillBlue(255), vgradAlpha(192), image.RGBAColor{81, 0, 102, 255}},
+}
+
+func TestDraw(t *testing.T) {
+	for _, test := range drawTests {
+		dst := hgradRed(255)
+		DrawMask(dst, Rect(0, 0, 16, 16), test.src, ZP, test.mask, ZP, SoverD)
+		if !eq(dst.At(8, 8), test.expected) {
+			t.Errorf("draw %s: %v versus %v", test.desc, dst.At(8, 8), test.expected)
+		}
+	}
+}