t.Fatalf("unexpected prefix: %q", out)
	}
	from, stale, err := p.TransformFromStorage(ctx, out, dataCtx)
	if err != nil {
		t.Fatal(err)
	}
	if stale || !bytes.Equal([]byte("firstvalue"), from) {
		t.Fatalf("unexpected data: %t %q", stale, from)
	}

	// verify changing the context fails storage
	_, _, err = p.TransformFromStorage(ctx, out, value.DefaultContext("incorrect_context"))
	if err != nil {