calculator.go

package main

import (
	"regexp"
	"strconv"
)

func Add(valueString string) int {
	if valueString == "" {
		return 0
	}
	re := regexp.MustCompile("^(//.*\n)")
	delimiter := "[,\n]"
	if re.MatchString(valueString) {
		delimiter = string(valueString[2])
		valueString = re.ReplaceAllString(valueString, "")
	}

	re = regexp.MustCompile(delimiter)
	value := re.Split(valueString, -1)

	sum := 0
	for i := 0; i < len(value); i++ {
		value, _ := strconv.Atoi(value[i])
		if value < 0 {
			panic("negatives not allowed")
		}
		sum += value
	}
	return sum
}
func main() {
	Add("")
}

calculator_test.go

package main

import "testing"

func TestEmptyShouldReturnZero(t *testing.T) {
	value := Add("")
	want := 0

	if value != want {
		t.Errorf("value %q want %q", value, want)
	}
}

func TestSingleValueShouldReturnSingleInt(t *testing.T) {
	value := Add("1")
	want := 1

	if value != want {
		t.Errorf("value %q want %q", value, want)
	}
}

func TestTwoValuesShouldReturnSum(t *testing.T) {
	value := Add("1,2")
	want := 3

	if value != want {
		t.Errorf("value %q want %q", value, want)
	}
}

func TestNValuesShouldReturnSum(t *testing.T) {
	value := Add("1,2,3,4,5,6,7,8,9")
	want := 45

	if value != want {
		t.Errorf("value %q want %q", value, want)
	}
}

func TestNValuesShouldReturnSumWithSpace(t *testing.T) {
	value := Add("1\n2,3")
	want := 6

	if value != want {
		t.Errorf("value %q want %q", value, want)
	}
}

func TestShouldCustomizeDemilimiter(t *testing.T) {
	value := Add("//;\n1;2")
	want := 3

	if value != want {
		t.Errorf("value %q want %q", value, want)
	}
}

func TestShouldNotAllowNegativeNumber(t *testing.T) {
	defer func() {
		if r := recover(); r != "negatives not allowed" {
			t.Error()
		}
	}()
	Add("-1")
}

gistfile1.txt

https://kata-log.rocks/string-calculator-kata