internal/processtest: add a test for #2620

Updates #2620

internal/processtest/testdata/issue2620.go

@@ -0,0 +1,41 @@
+// Copyright 2023 The Ebitengine Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//go:build ignore
+
+package main
+
+import (
+	"github.com/hajimehoshi/ebiten/v2"
+)
+
+type Game struct{}
+
+func (g *Game) Update() error {
+	return ebiten.Termination
+}
+
+func (g *Game) Draw(screen *ebiten.Image) {
+}
+
+func (g *Game) Layout(width, height int) (int, int) {
+	return 640, 480
+}
+
+func main() {
+	ebiten.SetRunnableOnUnfocused(false)
+	if err := ebiten.RunGame(&Game{}); err != nil {
+		panic(err)
+	}
+}