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Go 1.10: randutil_test.go:56: Sprintf call has arguments but no formatting directives

2bb1b66 does not pass Go 1.10 unit tests

+ GOPATH=/builddir/build/BUILD/randutil-2bb1b664bcff821e02b2a0644cd29c7e824d54f8/_build:/usr/share/gocode
+ go test -buildmode pie -compiler gc -ldflags '-extldflags '\''-Wl,-z,relro  '\'''
# github.com/jmcvetta/randutil
./randutil_test.go:56: Sprintf call has arguments but no formatting directives
FAIL    github.com/jmcvetta/randutil [build failed]

randutil.String doesn't pick the last character in a set

I wanted to test for any biases the string generator might have; sadly, it looks like the generator is strongly biased against the last character in a set - it never gets picked.

I wrote this test program:

package main

import (
    "os"
    "strconv"

    "fmt"

    "github.com/jmcvetta/randutil"
)

const (
    PasswordCharacters = "}~"
)

func main() {
    howmany, err := strconv.Atoi(os.Args[1])
    if err != nil {
        fmt.Printf("Need a password length, error %s\n", err)
        os.Exit(1)
    }
    length, err := strconv.Atoi(os.Args[2])
    if err != nil {
        fmt.Printf("Need a password count, error %s\n", err)
        os.Exit(1)
    }

    charWeights := make(map[rune]int)
    for _, c := range PasswordCharacters {
        charWeights[c] = 0
    }

    for i := 0; i < howmany; i++ {
        onePass, err := randutil.String(length, PasswordCharacters)
        if err != nil {
            fmt.Printf("Got error generating pass: %v\n", err)
        }
        for _, c := range onePass {
            charWeights[c]++
        }
    }
    for _, c := range PasswordCharacters {
        count := charWeights[c]
        fmt.Printf("%d\t%c\n", count, c)
    }
}