✨ (roman-numerals): add fith test and refactor

Author: yuanyu90221

property-base-test/roman_number.go

@@ -4,12 +4,18 @@ import "strings"
 
 func ConvertToRoman(arabic int) string {
 	var result strings.Builder
-	for i := arabic; i > 0; i-- {
-		if arabic == 4 {
+	for arabic > 0 {
+		switch {
+		case arabic > 4:
+			arabic -= 5
+			result.WriteString("V")
+		case arabic > 3:
+			arabic -= 4
 			result.WriteString("IV")
-			break
+		default:
+			arabic--
+			result.WriteString("I")
 		}
-		result.WriteString("I")
 	}
 	return result.String()
 }

property-base-test/roman_number_test.go

@@ -12,6 +12,7 @@ func TestRomanNumerals(t *testing.T) {
 		{"2 gets converted to II", 2, "II"},
 		{"3 gets converted to III", 3, "III"},
 		{"4 gets converted to IV", 4, "IV"},
+		{"5 gets converted to V", 5, "V"},
 	}
 
 	for _, test := range cases {