cmd/gogio: start using a TestDriver e2e interface

Now we implement the "red background" end-to-end test exactly once.

While at it, start using a 800x600 window size, which is a bit more
realistic than 600x600, and will catch if we got either dimension wrong.

The interface only has two methods for now, but it will be expanded in
the future to also support input such as clicks.

Keeping state in the test driver, such as a context or a connection, is
a bit awkward but necessary so that we don't have to repeat arguments
over and over. The same applies to testing.T.

Signed-off-by: Daniel Martí <mvdan@mvdan.cc>

cmd/gogio/js_test.go

@@ -6,7 +6,6 @@ import (
 	"bytes"
 	"context"
 	"errors"
-	"flag"
 	"image"
 	"image/png"
 	"io/ioutil"
@@ -23,23 +22,28 @@ import (
 	_ "gioui.org/unit" // the build tool adds it to go.mod, so keep it there
 )
 
-var headless = flag.Bool("headless", true, "run end-to-end tests in headless mode")
+type JSTestDriver struct {
+	t *testing.T
 
-func TestJSOnChrome(t *testing.T) {
-	t.Parallel()
+	// ctx is the chromedp context.
+	ctx context.Context
+}
+
+func (d *JSTestDriver) Start(t_ *testing.T, path string, width, height int) (cleanups []func()) {
+	d.t = t_
 
 	// First, build the app.
 	dir, err := ioutil.TempDir("", "gio-endtoend-js")
 	if err != nil {
-		t.Fatal(err)
+		d.t.Fatal(err)
 	}
-	defer os.RemoveAll(dir)
+	cleanups = append(cleanups, func() { os.RemoveAll(dir) })
 
 	// TODO(mvdan): This is inefficient, as we link the gogio tool every time.
 	// Consider options in the future. On the plus side, this is simple.
-	cmd := exec.Command("go", "run", ".", "-target=js", "-o="+dir, "testdata/red.go")
+	cmd := exec.Command("go", "run", ".", "-target=js", "-o="+dir, path)
 	if out, err := cmd.CombinedOutput(); err != nil {
-		t.Fatalf("could not build app: %s:\n%s", err, out)
+		d.t.Fatalf("could not build app: %s:\n%s", err, out)
 	}
 
 	// Second, start Chrome.
@@ -64,20 +68,21 @@ func TestJSOnChrome(t *testing.T) {
 	)
 
 	actx, cancel := chromedp.NewExecAllocator(context.Background(), opts...)
-	defer cancel()
+	cleanups = append(cleanups, cancel)
 
 	ctx, cancel := chromedp.NewContext(actx,
 		// Send all logf/errf calls to t.Logf
-		chromedp.WithLogf(t.Logf),
+		chromedp.WithLogf(d.t.Logf),
 	)
-	defer cancel()
+	cleanups = append(cleanups, cancel)
+	d.ctx = ctx
 
 	if err := chromedp.Run(ctx); err != nil {
 		if errors.Is(err, exec.ErrNotFound) {
-			t.Skipf("test requires Chrome to be installed: %v", err)
+			d.t.Skipf("test requires Chrome to be installed: %v", err)
 			return
 		}
-		t.Fatal(err)
+		d.t.Fatal(err)
 	}
 	chromedp.ListenTarget(ctx, func(ev interface{}) {
 		switch ev := ev.(type) {
@@ -91,7 +96,7 @@ func TestJSOnChrome(t *testing.T) {
 					}
 					args.Write(arg.Value)
 				}
-				t.Logf("console %s: %s", ev.Type, args.String())
+				d.t.Logf("console %s: %s", ev.Type, args.String())
 			}
 		}
 	})
@@ -99,46 +104,40 @@ func TestJSOnChrome(t *testing.T) {
 	// Third, serve the app folder, set the browser tab dimensions, and
 	// navigate to the folder.
 	ts := httptest.NewServer(http.FileServer(http.Dir(dir)))
-	defer ts.Close()
+	cleanups = append(cleanups, ts.Close)
 
 	if err := chromedp.Run(ctx,
-		// A small window with 2x HiDPI.
-		chromedp.EmulateViewport(300, 300, chromedp.EmulateScale(2.0)),
+		chromedp.EmulateViewport(int64(width), int64(height)),
 		chromedp.Navigate(ts.URL),
 	); err != nil {
-		t.Fatal(err)
+		d.t.Fatal(err)
 	}
 
-	// Finally, run the test.
-
-	// 1: Once the canvas is ready, grab a screenshot to check that the
-	//    entirety of the viewport is red, as per the background color.
-	var buf []byte
 	if err := chromedp.Run(ctx,
 		chromedp.WaitReady("canvas", chromedp.ByQuery),
+	); err != nil {
+		d.t.Fatal(err)
+	}
+
+	return cleanups
+}
+
+func (d *JSTestDriver) Screenshot() image.Image {
+	var buf []byte
+	if err := chromedp.Run(d.ctx,
 		chromedp.CaptureScreenshot(&buf),
 	); err != nil {
-		t.Fatal(err)
+		d.t.Fatal(err)
 	}
 	img, err := png.Decode(bytes.NewReader(buf))
 	if err != nil {
-		t.Fatal(err)
+		d.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, 0xdede, 0xadad, 0xbebe)
-	wantColor(t, img, 595, 595, 0xdede, 0xadad, 0xbebe)
+	return img
 }
 
-func wantColor(t *testing.T, img image.Image, x, y int, r, g, b uint32) {
-	color := img.At(x, y)
-	r_, g_, b_, _ := color.RGBA()
-	if r_ != r || g_ != g || b_ != b {
-		t.Errorf("got 0x%04x%04x%04x at (%d,%d), want 0x%04x%04x%04x",
-			r_, g_, b_, x, y, r, g, b)
-	}
+func TestJS(t *testing.T) {
+	t.Parallel()
+
+	runEndToEndTest(t, &JSTestDriver{})
 }