roman: add 4

roman/roman.go

@@ -9,5 +9,8 @@ func ConvertToRoman(arabic int) string {
 			converted.WriteString("I")
 		}
 	}
+	if arabic == 4 {
+		return "IV"
+	}
 	return converted.String()
 }

roman/roman_test.go

@@ -11,6 +11,7 @@ func TestRomanNemerals(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 {
 		t.Run(test.Description, func(t *testing.T) {