roman_go_roman_test.go

// roman_test.go
import (
	"fmt"
	"testing"
)

func TestToRoman(t *testing.T) {
	testCases := []struct {
		in   Arabian
		want string
	}{
		{1, "I"},
		{2, "II"},
		{5, "V"},
	}
	for _, test := range testCases {
		name := fmt.Sprintf("%v=>%vと変換できること", test.in, test.want)
		t.Run(name, func(t *testing.T) {
			if got := test.in.ToRoman(); got != test.want {
				t.Errorf("Arabian(%v).ToRoman(): got %v want %v", test.in, got, test.want)
			}
		})
	}
}

// roman.go
package roman

type Arabian uint16

func (in Arabian) ToRoman() string {
	numbers := []struct {
		arabian Arabian
		roman   string
	}{
		{5, "V"},
		{1, "I"},
	}
	var out string
	for remain := in; remain != 0; {
		for _, n := range numbers {
			if remain >= n.arabian {
				out += n.roman
				remain = remain - n.arabian
			}
		}
	}
	return out
}