test: add new digits overflow test

Author: replydev

src/otp/otp_element.rs

@@ -204,7 +204,7 @@ impl OTPElement {
         }
     }
 
-    pub fn format_code(&self, value: u32) -> Result<String, OtpError> {
+    fn format_code(&self, value: u32) -> Result<String, OtpError> {
         // Get the formatted code
         let exponential = 10_u32
             .checked_pow(self.digits as u32)
@@ -234,6 +234,7 @@ mod test {
     use crate::otp::otp_element::OTPType::Totp;
 
     use crate::otp::from_otp_uri::FromOtpUri;
+    use crate::otp::otp_error::OtpError;
 
     #[test]
     fn test_serialization_otp_uri_full_element() {
@@ -290,4 +291,28 @@ mod test {
         let otp_uri = "otpauth://totp/2Ponies%40Github%20No.1?secret=JBSWY3DPEHPK3PXP&algorithm=SHA1&digits=6&period=30&lock=false&issuer=test";
         assert_eq!(true, OTPElement::from_otp_uri(otp_uri).is_ok())
     }
+
+    #[test]
+    fn test_invalid_digits_should_not_overflow() {
+        // Arrange
+        let invalid_digits_value = 10;
+
+        let element = OTPElement {
+            secret: "xr5gh44x7bprcqgrdtulafeevt5rxqlbh5wvked22re43dh2d4mapv5g".to_uppercase(),
+            issuer: String::from("IssuerText"),
+            label: String::from("LabelText"),
+            digits: invalid_digits_value,
+            type_: Totp,
+            algorithm: Sha1,
+            period: 30,
+            counter: None,
+            pin: None,
+        };
+
+        // Act
+        let result = element.get_otp_code();
+
+        // Assert
+        assert_eq!(Err(OtpError::InvalidDigits), result)
+    }
 }