cmd/gogio: groundwork for Windows e2e tests on Wine

First, move from debian unstable to testing, since sway was promoted to
testing as of earlier this week.

Second, use the --sync option when using xdotool to move an X11 mouse.
This makes the command block until the mouse has finished moving to the
specified location, removing a potential race with the following
'xdotool click' command.

Third, deduplicate some logic into driverBase: tempDir to create a
temporary directory within a test, and needPrograms to skip a test if
the required programs aren't available.

Lastly, split the code that starts the X11 server into a method, so that
the future Wine e2e driver can reuse it. Since Wine is tightly coupled
with X11, we can reuse a good part of the code, including the X11 server
and the xdotool mechanisms.

We also add a TODO to perhaps improve the handling of the app's output
under each of the e2e test cases.

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

cmd/gogio/js_test.go

@@ -8,10 +8,8 @@ import (
 	"errors"
 	"image"
 	"image/png"
-	"io/ioutil"
 	"net/http"
 	"net/http/httptest"
-	"os"
 	"os/exec"
 	"strings"
 
@@ -34,12 +32,7 @@ func (d *JSTestDriver) Start(path string, width, height int) {
 	}
 
 	// First, build the app.
-	dir, err := ioutil.TempDir("", "gio-endtoend-js")
-	if err != nil {
-		d.Fatal(err)
-	}
-	d.Cleanup(func() { os.RemoveAll(dir) })
-
+	dir := d.tempDir("gio-endtoend-js")
 	// 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, path)