// See golang.org/issue/6563.
		pos := (*r.Expr).Pos()
		if x, ok := expr.(*ast.Ident); ok {
			expr = &ast.Ident{NamePos: pos, Name: x.Name}
		}

		// Change AST, because some later processing depends on it,
		// and also because -godefs mode still prints the AST.
		old := *r.Expr
		*r.Expr = expr

		// Record source-level edit for cgo output.
		if !r.Done {

	expect = "a to zed"
	if string(m) != expect {
		t.Errorf("rot13: expected %q got %q", expect, m)
	}

	// 5. Drop
	dropNotLatin := func(r rune) rune {
		if unicode.Is(unicode.Latin, r) {
			return r
		}
		return -1
	}
	m = Map(dropNotLatin, []byte("Hello, 세계"))
	expect = "Hello"
	if string(m) != expect {
		t.Errorf("drop: expected %q got %q", expect, m)
	}