test: retry TestWasm when Chrome does not start in time (#584)

TestWasm failed with "websocket url timeout reached" when Chrome took
more than 20s to print its DevTools address. On 20 fresh GitHub
runners the first Chrome start took 5.2s to 27.4s, and 3 took over
20s. Later starts took at most 1.2s. TestWasm now retries on that
error, up to 3 attempts.

Author: mafredri

conn_test.go

@@ -459,15 +459,25 @@ func TestWasm(t *testing.T) {
 	}))
 	defer s.Close()
 
-	ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
+	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Minute)
 	defer cancel()
 
-	cmd := exec.CommandContext(ctx, "go", "test", "-exec=wasmbrowsertest", ".", "-v")
-	cmd.Env = append(cleanEnv(os.Environ()), "GOOS=js", "GOARCH=wasm", fmt.Sprintf("WS_ECHO_SERVER_URL=%v", s.URL))
-
-	b, err := cmd.CombinedOutput()
-	if err != nil {
-		t.Fatalf("wasm test binary failed: %v:\n%s", err, b)
+	// Chrome's first start on a fresh CI runner can exceed the 20s that
+	// wasmbrowsertest allows. No wasm test has run by then, so retrying is safe.
+	const chromeStartTimeout = "websocket url timeout reached"
+	const attempts = 3
+	for attempt := 1; attempt <= attempts; attempt++ {
+		cmd := exec.CommandContext(ctx, "go", "test", "-exec=wasmbrowsertest", ".", "-v")
+		cmd.Env = append(cleanEnv(os.Environ()), "GOOS=js", "GOARCH=wasm", fmt.Sprintf("WS_ECHO_SERVER_URL=%v", s.URL))
+
+		b, err := cmd.CombinedOutput()
+		if err == nil {
+			return
+		}
+		if attempt == attempts || ctx.Err() != nil || !bytes.Contains(b, []byte(chromeStartTimeout)) {
+			t.Fatalf("wasm test binary failed: %v:\n%s", err, b)
+		}
+		t.Logf("attempt %d/%d: Chrome did not start in time, retrying", attempt, attempts)
 	}
 }