internal/processtest: remove TestShaderNoMain and add shadernomain.go

A shader compilation error breaks the state of the graphics command
queue, and this cannot be reused. Thus, a process test is appropriated.

internal/processtest/testdata/shadernomain.go

@@ -0,0 +1,57 @@
+// Copyright 2022 The Ebiten 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
+// +build ignore
+
+package main
+
+import (
+	"errors"
+
+	"github.com/hajimehoshi/ebiten/v2"
+)
+
+var regularTermination = errors.New("regular termination")
+
+type Game struct {
+	shader  *ebiten.Shader
+	timeout int
+}
+
+func (g *Game) Update() error {
+	// A shader compilation error breaks the state of the graphics command queue, and this cannot be reused.
+	// Thus, a process test is appropriated.
+	g.shader, _ = ebiten.NewShader([]byte(`package main`))
+	g.timeout++
+	if g.timeout > 60 {
+		return regularTermination
+	}
+	return nil
+}
+
+func (g *Game) Draw(screen *ebiten.Image) {
+	screen.DrawRectShader(1, 1, g.shader, nil)
+}
+
+func (g *Game) Layout(width, height int) (int, int) {
+	return width, height
+}
+
+func main() {
+	if err := ebiten.RunGame(&Game{}); err != nil && err != regularTermination {
+		return
+	}
+	panic("RunGame must return an error but not")
+}

shader_test.go

@@ -191,21 +191,6 @@ func Fragment(position vec4, texCoord vec2, color vec4) vec4 {
 	}
 }
 
-func TestShaderNoMain(t *testing.T) {
-	defer func() {
-		if r := recover(); r == nil {
-			t.Errorf("At must panic but not")
-		}
-	}()
-
-	const w, h = 16, 16
-	s, _ := ebiten.NewShader([]byte(`package main
-`))
-	dst := ebiten.NewImage(w, h)
-	dst.DrawRectShader(w, h, s, nil)
-	dst.At(0, 0)
-}
-
 func TestShaderUninitializedUniformVariables(t *testing.T) {
 	const w, h = 16, 16