Add App.WithFileSystem (#2638)

Signed-off-by: toyamagu-2021 <toyamagu2021@gmail.com>

pkg/app/app.go

@@ -103,6 +103,12 @@ func New(conf ConfigProvider) *App {
 	})
 }
 
+// WithFileSystem swaps the FileSystem this App reads through while loading state.
+func (a *App) WithFileSystem(fs *filesystem.FileSystem) *App {
+	a.fs = fs
+	return a
+}
+
 func Init(app *App) *App {
 	var err error
 	app.valsRuntime, err = plugins.ValsInstance()

pkg/app/app_test.go

@@ -48,6 +48,16 @@ func injectFs(app *App, fs *testhelper.TestFs) *App {
 	return app
 }
 
+func TestAppWithFileSystem(t *testing.T) {
+	app := &App{}
+	fs := ffs.DefaultFileSystem()
+
+	got := app.WithFileSystem(fs)
+
+	require.Same(t, app, got)
+	require.Same(t, fs, app.fs)
+}
+
 func expectNoCallsToHelm(app *App) {
 	expectNoCallsToHelmVersion(app)
 }