panic: invalid argument to Intn

goroutine 1 [running]:
math/rand.(*Rand).Intn(0x400007ac38?, 0xbb9c4?)
	/usr/local/go/src/math/rand/rand.go:180 +0x64
math/rand.Intn(0x0)
	/usr/local/go/src/math/rand/rand.go:453 +0x28
main.genTest()
	/tmp/cf-worker-596298479/verifierK.go:59 +0x50
main.main()
	/tmp/cf-worker-596298479/verifierK.go:94 +0x1e0