godebugtester run -work main.go
contains stdout "\"20 []\"=(f2())"

-- main.go --
package main
import "fmt"
func main(){
	_=f2()
}
func f1() int{
	_=7
	return 1
}
func f2() string{
	_=5
	u := []int{9,1,2,3}
	_=5
	if 1 >= f1() && 1 <= f1() {
		b := 10
		u = u[:1-f1()]
		a := 10 + b
		return fmt.Sprintf("%v %v", a, u)
	}
	_=8
	return "aa"
}