panic: invalid argument to Intn

goroutine 1 [running]:
math/rand.(*Rand).Intn(0x400009cc78?, 0x19ee8?)
	/usr/local/go/src/math/rand/rand.go:180 +0x64
main.genTest(0x400009ce90)
	/tmp/cf-worker-348284147/verifierG.go:254 +0x60
main.main()
	/tmp/cf-worker-348284147/verifierG.go:324 +0x194