diff --git a/cmd/go.mod b/cmd/go.mod
index 86699fe5..ca231580 100644
--- a/cmd/go.mod
+++ b/cmd/go.mod
@@ -4,6 +4,10 @@ go 1.13
 
 require (
 	gioui.org v0.0.0-20191029130630-4641607cd6a4
+	github.com/BurntSushi/freetype-go v0.0.0-20160129220410-b763ddbfe298 // indirect
+	github.com/BurntSushi/graphics-go v0.0.0-20160129215708-b43f31a4a966 // indirect
+	github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802
+	github.com/BurntSushi/xgbutil v0.0.0-20190907113008-ad855c713046
 	github.com/chromedp/cdproto v0.0.0-20191009033829-c22f49c9ff0a
 	github.com/chromedp/chromedp v0.5.1
 	golang.org/x/image v0.0.0-20190802002840-cff245a6509b
diff --git a/cmd/go.sum b/cmd/go.sum
index 122d738c..2ff656c9 100644
--- a/cmd/go.sum
+++ b/cmd/go.sum
@@ -1,7 +1,14 @@
 dmitri.shuralyov.com/gpu/mtl v0.0.0-20190408044501-666a987793e9/go.mod h1:H6x//7gZCb22OMCxBHrMx7a5I7Hp++hsVxbQ4BYO7hU=
 gioui.org v0.0.0-20191029130630-4641607cd6a4 h1:WKYMON5AGU5/Xs5ezSWq9i/hiobSXBsQlsPSVXybScM=
 gioui.org v0.0.0-20191029130630-4641607cd6a4/go.mod h1:KqFFi2Dq5gYA3FJ0sDOt8OBXoMsuxMtE8v2f0JExXAY=
+github.com/BurntSushi/freetype-go v0.0.0-20160129220410-b763ddbfe298 h1:1qlsVAQJXZHsaM8b6OLVo6muQUQd4CwkH/D3fnnbHXA=
+github.com/BurntSushi/freetype-go v0.0.0-20160129220410-b763ddbfe298/go.mod h1:D+QujdIlUNfa0igpNMk6UIvlb6C252URs4yupRUV4lQ=
+github.com/BurntSushi/graphics-go v0.0.0-20160129215708-b43f31a4a966 h1:lTG4HQym5oPKjL7nGs+csTgiDna685ZXjxijkne828g=
+github.com/BurntSushi/graphics-go v0.0.0-20160129215708-b43f31a4a966/go.mod h1:Mid70uvE93zn9wgF92A/r5ixgnvX8Lh68fxp9KQBaI0=
+github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802 h1:1BDTz0u9nC3//pOCMdNH+CiXJVYJh5UQNCOBG7jbELc=
 github.com/BurntSushi/xgb v0.0.0-20160522181843-27f122750802/go.mod h1:IVnqGOEym/WlBOVXweHU+Q+/VP0lqqI8lqeDx9IjBqo=
+github.com/BurntSushi/xgbutil v0.0.0-20190907113008-ad855c713046 h1:O/r2Sj+8QcMF7V5IcmiE2sMFV2q3J47BEirxbXJAdzA=
+github.com/BurntSushi/xgbutil v0.0.0-20190907113008-ad855c713046/go.mod h1:uw9h2sd4WWHOPdJ13MQpwK5qYWKYDumDqxWWIknEQ+k=
 github.com/chromedp/cdproto v0.0.0-20191009033829-c22f49c9ff0a h1:AuIGvB6IuWpMEdfKQ+t77D6dzLpNftzxAsktehYyWn8=
 github.com/chromedp/cdproto v0.0.0-20191009033829-c22f49c9ff0a/go.mod h1:PfAWWKJqjlGFYJEidUM6aVIWPr0EpobeyVWEEmplX7g=
 github.com/chromedp/chromedp v0.5.1 h1:PAqhoCWCHzRphYnmmxLSiYk7EEwDplCm4woTCCaV2cQ=
diff --git a/cmd/gogio/js_test.go b/cmd/gogio/js_test.go
index c348d19e..88bbdad8 100644
--- a/cmd/gogio/js_test.go
+++ b/cmd/gogio/js_test.go
@@ -7,6 +7,7 @@ import (
 	"context"
 	"errors"
 	"flag"
+	"image"
 	"image/png"
 	"io/ioutil"
 	"net/http"
@@ -25,6 +26,8 @@ import (
 var headless = flag.Bool("headless", true, "run end-to-end tests in headless mode")
 
 func TestJSOnChrome(t *testing.T) {
+	t.Parallel()
+
 	// First, build the app.
 	dir, err := ioutil.TempDir("", "gio-endtoend-js")
 	if err != nil {
@@ -124,14 +127,15 @@ func TestJSOnChrome(t *testing.T) {
 		t.Fatalf("expected dimensions to be %d*%d, got %d*%d",
 			wantSize, wantSize, size.X, size.Y)
 	}
-	wantColor := func(x, y int, r, g, b, a uint32) {
-		color := img.At(x, y)
-		r_, g_, b_, a_ := color.RGBA()
-		if r_ != r || g_ != g || b_ != b || a_ != a {
-			t.Errorf("got 0x%04x%04x%04x%04x at (%d,%d), want 0x%04x%04x%04x%04x",
-				r_, g_, b_, a_, x, y, r, g, b, a)
-		}
-	}
-	wantColor(5, 5, 0xffff, 0x0, 0x0, 0xffff)
-	wantColor(595, 595, 0xffff, 0x0, 0x0, 0xffff)
+	wantColor(t, img, 5, 5, 0xffff, 0x0, 0x0, 0xffff)
+	wantColor(t, img, 595, 595, 0xffff, 0x0, 0x0, 0xffff)
+}
+
+func wantColor(t *testing.T, img image.Image, x, y int, r, g, b, a uint32) {
+	color := img.At(x, y)
+	r_, g_, b_, a_ := color.RGBA()
+	if r_ != r || g_ != g || b_ != b || a_ != a {
+		t.Errorf("got 0x%04x%04x%04x%04x at (%d,%d), want 0x%04x%04x%04x%04x",
+			r_, g_, b_, a_, x, y, r, g, b, a)
+	}
 }
diff --git a/cmd/gogio/main_test.go b/cmd/gogio/main_test.go
index 4baa1128..efb441e0 100644
--- a/cmd/gogio/main_test.go
+++ b/cmd/gogio/main_test.go
@@ -9,6 +9,8 @@ type expval struct {
 }
 
 func TestAppID(t *testing.T) {
+	t.Parallel()
+
 	tests := []expval{
 		{"example", "localhost.example"},
 		{"example.com", "com.example"},
diff --git a/cmd/gogio/x11_test.go b/cmd/gogio/x11_test.go
new file mode 100644
index 00000000..cdc552e8
--- /dev/null
+++ b/cmd/gogio/x11_test.go
@@ -0,0 +1,151 @@
+// SPDX-License-Identifier: Unlicense OR MIT
+
+// TODO(mvdan): come up with an end-to-end platform interface, including methods
+// like "take screenshot" or "close app", so that we can run the same tests on
+// all supported platforms without writing them many times.
+
+package main_test
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/BurntSushi/xgb"
+	"github.com/BurntSushi/xgb/xproto"
+	"github.com/BurntSushi/xgbutil"
+	"github.com/BurntSushi/xgbutil/xgraphics"
+)
+
+func TestX11(t *testing.T) {
+	t.Parallel()
+
+	// TODO(mvdan): pick a random one between a large pool, and retry if
+	// it's already taken.
+	const display = ":15"
+
+	var xprog string
+	xflags := []string{"-wr"}
+	if *headless {
+		xprog = "Xvfb" // virtual X server
+		xflags = append(xflags, "-screen", "0", "600x600x24")
+	} else {
+		xprog = "Xephyr" // nested X server as a window
+		xflags = append(xflags, "-screen", "600x600")
+	}
+	xflags = append(xflags, display)
+	if _, err := exec.LookPath(xprog); err != nil {
+		t.Skipf("%s needed to run with -headless=%t", xprog, *headless)
+	}
+
+	// First, build the app.
+	dir, err := ioutil.TempDir("", "gio-endtoend-x11")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(dir)
+
+	bin := filepath.Join(dir, "red")
+	cmd := exec.Command("go", "build", "-o="+bin, "testdata/red.go")
+	if out, err := cmd.CombinedOutput(); err != nil {
+		t.Fatalf("could not build app: %s:\n%s", err, out)
+	}
+
+	var wg sync.WaitGroup
+	defer wg.Wait()
+
+	// First, start the X server.
+	{
+		ctx, cancel := context.WithCancel(context.Background())
+		cmd := exec.CommandContext(ctx, xprog, xflags...)
+		out := &bytes.Buffer{}
+		cmd.Stdout = out
+		cmd.Stderr = out
+		if err := cmd.Start(); err != nil {
+			t.Fatal(err)
+		}
+		defer cancel()
+		// TODO(mvdan): properly wait for the display to be ready instead.
+		time.Sleep(200 * time.Millisecond)
+		wg.Add(1)
+		go func() {
+			if err := cmd.Wait(); err != nil && ctx.Err() == nil {
+				// Print all output and error.
+				io.Copy(os.Stdout, out)
+				t.Error(err)
+			}
+			wg.Done()
+		}()
+	}
+
+	// Then, start our program on the X server above.
+	{
+		ctx, cancel := context.WithCancel(context.Background())
+		cmd := exec.CommandContext(ctx, bin)
+		out := &bytes.Buffer{}
+		cmd.Env = append(os.Environ(), "DISPLAY="+display)
+		cmd.Stdout = out
+		cmd.Stderr = out
+		if err := cmd.Start(); err != nil {
+			t.Fatal(err)
+		}
+		defer cancel()
+		wg.Add(1)
+		go func() {
+			if err := cmd.Wait(); err != nil && ctx.Err() == nil {
+				// Print all output and error.
+				io.Copy(os.Stdout, out)
+				t.Error(err)
+			}
+			wg.Done()
+		}()
+	}
+
+	// Finally, run our tests. A connection to the X server is used to
+	// interact with it.
+	{
+		if !testing.Verbose() {
+			xgb.Logger.SetOutput(ioutil.Discard)
+			xgbutil.Logger.SetOutput(ioutil.Discard)
+		}
+		xu, err := xgbutil.NewConnDisplay(display)
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer func() {
+			xu.Conn().Close()
+			// TODO(mvdan): Figure out a way to remove this sleep
+			// without introducing a panic. The xgb code will
+			// encounter a panic if the Xorg server exits before xgb
+			// has shut down fully.
+			// See: https://github.com/BurntSushi/xgb/pull/44
+			time.Sleep(20 * time.Millisecond)
+		}()
+
+		// Wait for the gio app to render.
+		// TODO(mvdan): do this properly, e.g. via waiting for log lines
+		// from the gio program.
+		time.Sleep(200 * time.Millisecond)
+
+		img, err := xgraphics.NewDrawable(xu, xproto.Drawable(xu.RootWin()))
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		size := img.Bounds().Size()
+		wantSize := 600 // 300px at 2.0 scaling factor
+		if size.X != wantSize || size.Y != wantSize {
+			t.Fatalf("expected dimensions to be %d*%d, got %d*%d",
+				wantSize, wantSize, size.X, size.Y)
+		}
+		wantColor(t, img, 5, 5, 0xffff, 0x0, 0x0, 0xffff)
+		wantColor(t, img, 595, 595, 0xffff, 0x0, 0x0, 0xffff)
+	}
+}