kata roman numerals in Go

Makefile

all: testAndCover

testAndCover:
	@go test -coverprofile=cover.out .
	@go tool cover -html=cover.out

romannumerals.go

package main

import "strings"

var romanLetter map[string]int
var romanNum map[int]string
var romanNumKeys []int

func init() {
	romanLetter = make(map[string]int)
	romanLetter["I"] = 1
	romanLetter["V"] = 5
	romanLetter["X"] = 10

	romanNum = make(map[int]string)
	romanNum[10] = "X"
	romanNum[5] = "V"
	romanNum[1] = "I"

	romanNumKeys = []int{10, 5, 1}
}

func romanSum(op1 string, op2 string) string {
	var sumRest int
	var sum string
	sum = ""
	sumRest = opSum(op1) + opSum(op2)

	if sumRest == 4 {
		return "IV"
	} else if sumRest == 9 {
		return "IX"
	}
	for _, n := range romanNumKeys {
		for sumRest >= n {
			sum = sum + romanNum[n]
			sumRest = sumRest - n
		}
	}
	return sum
}

func opSum(op string) int {
	if op == "IV" {
		return 4
	} else if op == "IX" {
		return 9
	} else {
		var opsum int
		opsum = 0
		for key, value := range romanLetter {
			opsum = opsum + strings.Count(op, key)*value
		}
		return opsum
	}
}

romannumerals_test.go

package main

import "testing"

func TestSum(t *testing.T) {
	cases := []struct {
		op1 string
		op2 string
		exp string
	}{
		{"I", "I", "II"},
		{"I", "II", "III"},
		{"II", "I", "III"},
		{"II", "II", "IV"},
		{"III", "I", "IV"},
		{"I", "III", "IV"},
		{"III", "II", "V"},
		{"II", "III", "V"},
		{"IV", "I", "V"},
		{"I", "IV", "V"},
		{"III", "III", "VI"},
		{"III", "IV", "VII"},
		{"III", "V", "VIII"},
		{"III", "VI", "IX"},
		{"V", "V", "X"},
		{"IX", "I", "X"},
		{"X", "I", "XI"},
	}
	for _, c := range cases {
		sum := romanSum(c.op1, c.op2)
		if sum != c.exp {
			t.Errorf("op1(%q) + op2(%q) = got(%q) != want(%q)", c.op1, c.op2, sum, c.exp)
		}
	}
}