stringcalculator in go

stringcalculator.go

package calculator

import (
	"errors"
	"fmt"
	"strconv"
	"strings"
)

func Add(numbers string) (int, error) {
	separators := ",\n"
	if strings.HasPrefix(numbers, "//") {
		if nli := strings.Index(numbers, "\n"); nli > 1 {
			separators = numbers[2 : nli+1]
			numbers = numbers[nli:len(numbers)]
		}
	}
	splitter := func(r rune) bool {
		return strings.ContainsRune(separators, r)
	}
	result := 0
	negatives := make([]int, 0)
	for _, v := range strings.FieldsFunc(numbers, splitter) {
		i, e := strconv.Atoi(v)
		if e == nil && i >= 0 {
			result += i
		} else if i < 0 {
			negatives = append(negatives, i)
		} else {
			return 0, nil
		}
	}
	if len(negatives) > 0 {
		return 0, errors.New(fmt.Sprintf("negatives not allowed %v", negatives))
	}
	return result, nil
}

stringcalculator_test.go

package calculator

import (
  "strconv"
  "testing"
)

func assert(input string, expected int, t *testing.T) {
	if output, _ := Add(input); output != expected {
		t.Errorf("Add(\"%v\") = %v, want %v", input, output, expected)
	}
}

func TestEmpty(t *testing.T) {
	assert("", 0, t)
}
func TestAdd(t *testing.T) {
	assert("1", 1, t)
}
func TestSingleNumber(t *testing.T) {
	a := []int{1, 2, 3, 10, 100, 1000, 10000}
	for _, v := range a {
		assert(strconv.Itoa(v), v, t)
	}
}

func TestInvalidInput(t *testing.T) {
	assert("a", 0, t)
}
func TestTwoNumbers(t *testing.T) {
	assert("1,2", 3, t)
}
func TestMoreNumbers(t *testing.T) {
	assert("1,2,3,4,10,100", 120, t)
}
func TestNewLine(t *testing.T) {
	assert("1\n2,3", 6, t)
}
func TestSpecifyDelimeter(t *testing.T) {
	assert("//;\n1;2", 3, t)
}
func TestNegatives(t *testing.T) {
	if _, e := Add("-1,-12"); e.Error() != "negatives not allowed [-1 -12]" {
		t.Errorf("Expecting error message: 'negatives not allowed [-1 -12]' got: '%s'", e.Error())
	}
}