✨ (roman_numerals): add fourth test and refactor

Author: yuanyu90221

property-base-test/roman_number.go

@@ -5,6 +5,10 @@ import "strings"
 func ConvertToRoman(arabic int) string {
 	var result strings.Builder
 	for i := arabic; i > 0; i-- {
+		if arabic == 4 {
+			result.WriteString("IV")
+			break
+		}
 		result.WriteString("I")
 	}
 	return result.String()

property-base-test/roman_number_test.go

@@ -11,6 +11,7 @@ func TestRomanNumerals(t *testing.T) {
 		{"1 gets converted to I", 1, "I"},
 		{"2 gets converted to II", 2, "II"},
 		{"3 gets converted to III", 3, "III"},
+		{"4 gets converted to IV", 4, "IV"},
 	}
 
 	for _, test := range cases {