diff --git a/src/messages.rs b/src/messages.rs
index 79db8f0..45c5b36 100644
--- a/src/messages.rs
+++ b/src/messages.rs
@@ -1,10 +1,10 @@
 pub const COUNTER_INVALID: &str = "Counter must be greater than or equal to 1";
 pub const DRIFT_BEHIND_INVALID: &str = "Drift behind must be less than timestamp";
 pub const INTERVAL_INVALID: &str = "Interval must be greater than or equal to 30";
-pub const OTP_LENGTH_INVALID: &str = "OTP length must be greater than or equal to 4";
+pub const OTP_LENGTH_INVALID: &str = "OTP length must be greater than or equal to 1";
 pub const OTP_LENGTH_NOT_MATCHED: &str = "OTP length does not match the length of the configuration";
-pub const PROV_OTP_LENGTH_INVALID: &str = "HOTP length must be 6";
-pub const PROV_OTP_RADIX_INVALID: &str = "HOTP radix must be 10";
+pub const PROV_OTP_LENGTH_INVALID: &str = "OTP length must be 6";
+pub const PROV_OTP_RADIX_INVALID: &str = "Radix must be 10";
 pub const RADIX_INVALID: &str = "Radix must be between 2 and 36 inclusive";
 pub const SECRET_EMPTY: &str = "Secret must not be empty";
 pub const TIMESTAMP_INVALID: &str = "Timestamp must be greater than or equal to 1";
diff --git a/src/otp/algorithm.rs b/src/otp/algorithm.rs
index ed8669c..ff9b3e4 100644
--- a/src/otp/algorithm.rs
+++ b/src/otp/algorithm.rs
@@ -10,6 +10,7 @@ pub trait AlgorithmTrait {
     fn hash(&self, secret: Vec<u8>, data: u64) -> Result<Vec<u8>, String>;
 }
 
+#[derive(Copy, Clone)]
 pub enum Algorithm {
     SHA1,
     SHA256,
diff --git a/src/otp/hotp.rs b/src/otp/hotp.rs
index dcb2f27..69566da 100644
--- a/src/otp/hotp.rs
+++ b/src/otp/hotp.rs
@@ -1,6 +1,6 @@
 use crate::messages::{
-    OTP_LENGTH_INVALID, OTP_LENGTH_NOT_MATCHED, PROV_OTP_LENGTH_INVALID,
-    PROV_OTP_RADIX_INVALID, RADIX_INVALID, SECRET_EMPTY, UNSUPPORTED_ALGORITHM,
+    OTP_LENGTH_INVALID, OTP_LENGTH_NOT_MATCHED, PROV_OTP_LENGTH_INVALID, PROV_OTP_RADIX_INVALID,
+    RADIX_INVALID, SECRET_EMPTY, UNSUPPORTED_ALGORITHM,
 };
 use crate::otp::algorithm::Algorithm;
 use crate::otp::otp::otp;
@@ -21,7 +21,7 @@ impl HOTP {
     ) -> Result<HOTP, &'static str> {
         if secret.len() < 1 {
             Err(SECRET_EMPTY)
-        } else if length < 4 {
+        } else if length < 1 {
             Err(OTP_LENGTH_INVALID)
         } else if radix < 2 || radix > 36 {
             Err(RADIX_INVALID)
@@ -45,12 +45,7 @@ impl HOTP {
         )
     }
 
-    pub fn verify(
-        &self,
-        otp: &str,
-        counter: u64,
-        retries: u64,
-    ) -> Result<Option<u64>, String> {
+    pub fn verify(&self, otp: &str, counter: u64, retries: u64) -> Result<Option<u64>, String> {
         if self.length != otp.len() as u8 {
             Err(OTP_LENGTH_NOT_MATCHED.to_string())
         } else {
diff --git a/src/otp/otp.rs b/src/otp/otp.rs
index 26d1cdb..67f4185 100644
--- a/src/otp/otp.rs
+++ b/src/otp/otp.rs
@@ -1,4 +1,4 @@
-use crate::messages::{COUNTER_INVALID, OTP_LENGTH_INVALID, RADIX_INVALID, SECRET_EMPTY};
+use crate::messages::COUNTER_INVALID;
 
 use crate::otp::algorithm::{Algorithm, AlgorithmTrait};
 use num_bigint::BigUint;
@@ -11,13 +11,7 @@ pub(crate) fn otp(
     radix: u8,
     counter: u64,
 ) -> Result<String, String> {
-    if secret.len() < 1 {
-        Err(SECRET_EMPTY.to_string())
-    } else if length < 4 {
-        Err(OTP_LENGTH_INVALID.to_string())
-    } else if radix < 2 || radix > 36 {
-        Err(RADIX_INVALID.to_string())
-    } else if counter < 1 {
+    if counter < 1 {
         Err(COUNTER_INVALID.to_string())
     } else {
         match otp_bin_code(algorithm, secret, counter) {
diff --git a/tests/hotp.rs b/tests/hotp.rs
index f2972db..ba8037c 100644
--- a/tests/hotp.rs
+++ b/tests/hotp.rs
@@ -1,35 +1,70 @@
-use rusotp::Algorithm;
+use rusotp::{generate_hotp, Algorithm, HOTP};
+
+const SECRET: &str = "12345678901234567890";
 
 #[test]
 fn fail_with_empty_secret() {
-    let result = rusotp::HOTP::new(Algorithm::SHA256, "", 1, 1);
+    let result = HOTP::new(Algorithm::SHA256, "", 1, 1);
     assert!(result.is_err(), "Expected an error");
     assert_eq!(result.err().unwrap(), "Secret must not be empty");
 }
 
 #[test]
-fn fail_with_invalid_otp_length() {
-    let result = rusotp::HOTP::new(Algorithm::SHA256, "12312341234", 1, 10);
+#[should_panic(expected = "Secret must not be empty")]
+fn generate_hotp_should_fail_with_empty_secret() {
+    generate_hotp(Algorithm::SHA256, "", 1, 1, 0);
+}
+
+#[test]
+fn fail_with_otp_length_less_than_1() {
+    let result = HOTP::new(Algorithm::SHA256, SECRET, 0, 10);
     assert!(result.is_err(), "Expected an error");
     assert_eq!(
         result.err().unwrap(),
-        "OTP length must be greater than or equal to 4"
+        "OTP length must be greater than or equal to 1"
     );
 }
 
 #[test]
-fn fail_with_invalid_radix() {
-    let result = rusotp::HOTP::new(Algorithm::SHA256, "12312341234", 4, 1);
-    assert!(result.is_err(), "Expected an error");
+#[should_panic(expected = "OTP length must be greater than or equal to 1")]
+fn generate_hotp_should_fail_otp_length_less_than_1() {
+    generate_hotp(Algorithm::SHA256, SECRET, 0, 10, 0);
+}
+
+#[test]
+fn fail_with_radix_less_than_2() {
+    let lesser_radix = HOTP::new(Algorithm::SHA256, SECRET, 4, 1);
+    assert!(lesser_radix.is_err(), "Expected an error");
     assert_eq!(
-        result.err().unwrap(),
+        lesser_radix.err().unwrap(),
+        "Radix must be between 2 and 36 inclusive"
+    );
+}
+
+#[test]
+#[should_panic(expected = "Radix must be between 2 and 36 inclusive")]
+fn generate_hotp_should_fail_radix_less_than_2() {
+    generate_hotp(Algorithm::SHA256, SECRET, 4, 1, 0);
+}
+#[test]
+fn fail_with_radix_greater_than_36() {
+    let greater_radix = HOTP::new(Algorithm::SHA256, SECRET, 4, 37);
+    assert!(greater_radix.is_err(), "Expected an error");
+    assert_eq!(
+        greater_radix.err().unwrap(),
         "Radix must be between 2 and 36 inclusive"
     );
 }
 
 #[test]
-fn fail_with_invalid_counter() {
-    let hotp = match rusotp::HOTP::new(Algorithm::SHA256, "12312341234", 4, 10) {
+#[should_panic(expected = "Radix must be between 2 and 36 inclusive")]
+fn generate_hotp_should_fail_radix_more_than_36() {
+    generate_hotp(Algorithm::SHA256, SECRET, 4, 37, 0);
+}
+
+#[test]
+fn fail_with_counter_less_than_1() {
+    let hotp = match HOTP::new(Algorithm::SHA256, SECRET, 4, 10) {
         Ok(hotp) => hotp,
         Err(e) => panic!("{}", e),
     };
@@ -44,12 +79,14 @@ fn fail_with_invalid_counter() {
 }
 
 #[test]
-fn fail_with_otp_length_not_matched() {
-    let hotp = match rusotp::HOTP::new(Algorithm::SHA256, "12312341234", 4, 10) {
-        Ok(hotp) => hotp,
-        Err(e) => panic!("{}", e),
-    };
+#[should_panic(expected = "Counter must be greater than or equal to 1")]
+fn generate_hotp_should_fail_with_counter_less_than_1() {
+    generate_hotp(Algorithm::SHA256, SECRET, 4, 10, 0);
+}
 
+#[test]
+fn fail_with_otp_length_not_matched() {
+    let hotp = HOTP::new(Algorithm::SHA256, SECRET, 4, 10).unwrap();
     let result = hotp.verify("12345", 10, 0);
 
     assert!(result.is_err(), "Expected an error");
@@ -61,8 +98,34 @@ fn fail_with_otp_length_not_matched() {
 
 #[test]
 fn generated_otp_is_correct() {
-    let secret = "12345678901234567890";
+    let data = vec![
+        (6, 10, 1, "247374"),
+        (6, 10, 2, "254785"),
+        (6, 10, 3, "496144"),
+        (6, 16, 1, "687B4E"),
+        (6, 24, 1, "N7C1B6"),
+        (6, 36, 1, "M16ONI"),
+        (8, 10, 100, "93583477"),
+        (8, 16, 100, "23615D75"),
+        (8, 24, 100, "032D2EKL"),
+        (8, 36, 100, "009TEJXX"),
+        (4, 36, 1, "6ONI"),
+        (4, 36, 2, "KYWX"),
+        (4, 36, 3, "ERBK"),
+        (4, 36, 4, "ROTO"),
+    ];
+
+    data.iter().for_each(|(length, radix, counter, otp)| {
+        let hotp = HOTP::new(Algorithm::SHA256, SECRET, *length, *radix).unwrap();
+
+        let result = hotp.generate(*counter);
+        assert!(result.is_ok(), "Expected a result");
+        assert_eq!(result.unwrap(), otp.to_string());
+    });
+}
 
+#[test]
+fn wrong_otp_does_not_get_verified() {
     let data = vec![
         (6, 10, 1, "247374"),
         (6, 10, 2, "254785"),
@@ -81,53 +144,143 @@ fn generated_otp_is_correct() {
     ];
 
     data.iter().for_each(|(length, radix, counter, otp)| {
-        match rusotp::HOTP::new(Algorithm::SHA256, secret, *length, *radix) {
-            Ok(hotp) => {
-                let result = hotp.generate(*counter);
-                assert!(result.is_ok(), "Expected a result");
-                assert_eq!(result.unwrap(), otp.to_string());
-            }
-            Err(e) => panic!("{}", e),
-        };
+        let hotp = HOTP::new(Algorithm::SHA256, SECRET, *length, *radix).unwrap();
+
+        let result = hotp.verify(otp, *counter + 1, 0);
+        assert!(result.is_ok(), "Expected a result");
+        assert!(result.unwrap().is_none(), "Expected a failed verification");
     });
 }
 
+#[test]
+fn otp_get_verified_with_retries() {
+    let data = vec![
+        (6, 10, 2, "254785", 1),
+        (6, 10, 3, "496144", 1),
+        (8, 10, 100, "93583477", 5),
+        (8, 16, 100, "23615D75", 1),
+        (8, 24, 100, "032D2EKL", 1),
+        (8, 36, 100, "009TEJXX", 1),
+        (4, 36, 2, "KYWX", 1),
+        (4, 36, 3, "ERBK", 1),
+        (4, 36, 4, "ROTO", 1),
+    ];
+
+    data.iter()
+        .for_each(|(length, radix, counter, otp, retries)| {
+            let hotp = HOTP::new(Algorithm::SHA256, SECRET, *length, *radix).unwrap();
+
+            let result = hotp.verify(otp, *counter - *retries, *retries);
+            assert!(result.is_ok(), "Expected a result");
+            assert!(
+                result.unwrap().is_some(),
+                "Expected a successful verification"
+            );
+        });
+}
+
 #[test]
 fn generated_otp_gets_verified() {
     let secret = "12345678901234567890";
 
     let data = vec![
-        (6, 10, 1),
-        (6, 10, 2),
-        (6, 10, 3),
-        (6, 16, 1),
-        (6, 24, 1),
-        (6, 36, 1),
-        (8, 10, 100),
-        (8, 16, 100),
-        (8, 24, 100),
-        (8, 36, 100),
-        (4, 36, 1),
-        (4, 36, 2),
-        (4, 36, 3),
+        (Algorithm::SHA256, 6, 10, 1),
+        (Algorithm::SHA256, 6, 10, 2),
+        (Algorithm::SHA256, 6, 10, 3),
+        (Algorithm::SHA256, 6, 16, 1),
+        (Algorithm::SHA256, 6, 24, 1),
+        (Algorithm::SHA256, 6, 36, 1),
+        (Algorithm::SHA256, 8, 10, 100),
+        (Algorithm::SHA256, 8, 16, 100),
+        (Algorithm::SHA256, 8, 24, 100),
+        (Algorithm::SHA256, 8, 36, 100),
+        (Algorithm::SHA256, 4, 36, 1),
+        (Algorithm::SHA256, 4, 36, 2),
+        (Algorithm::SHA256, 4, 36, 3),
     ];
 
-    data.iter().for_each(|(length, radix, counter)| {
-        match rusotp::HOTP::new(Algorithm::SHA256, secret, *length, *radix) {
-            Ok(hotp) => {
-                match hotp.generate(*counter) {
-                    Ok(otp) => {
-                        let result = hotp.verify(&otp, *counter, 0);
-                        assert!(result.is_ok(), "Expected a result");
-                        assert!(
-                            result.unwrap().is_some(),
-                            "Expected a successful verification"
-                        );
-                    }
-                    Err(e) => panic!("{}", e),
-                };
-            }
-            Err(e) => panic!("{}", e),
-        };
+    data.iter().for_each(|(algorithm, length, radix, counter)| {
+        let hotp = HOTP::new(*algorithm, secret, *length, *radix).unwrap();
+        let otp = hotp.generate(*counter).unwrap();
+
+        let result = hotp.verify(&otp, *counter, 0);
+        assert!(result.is_ok(), "Expected a result");
+        assert!(
+            result.unwrap().is_some(),
+            "Expected a successful verification"
+        );
     });
 }
+
+#[test]
+fn provisioning_uri_is_correct() {
+    let hotp_tool = HOTP::new(Algorithm::SHA1, SECRET, 6, 10).unwrap();
+
+    let result = hotp_tool.provisioning_uri("test", 0);
+
+    assert!(result.is_ok(), "Expected a result");
+    assert_eq!(
+        result.unwrap(),
+        "otpauth://hotp/test?secret=12345678901234567890&counter=0"
+    );
+}
+
+#[test]
+fn fail_provisioning_uri_with_sha256() {
+    let hotp_tool = HOTP::new(Algorithm::SHA256, SECRET, 6, 10).unwrap();
+
+    let result = hotp_tool.provisioning_uri("test", 0);
+
+    assert!(result.is_err(), "Expected an error");
+    assert_eq!(result.err().unwrap(), "Unsupported algorithm");
+}
+
+#[test]
+fn fail_provisioning_uri_with_sha512() {
+    let hotp_tool = HOTP::new(Algorithm::SHA512, SECRET, 6, 10).unwrap();
+
+    let result = hotp_tool.provisioning_uri("test", 0);
+
+    assert!(result.is_err(), "Expected an error");
+    assert_eq!(result.err().unwrap(), "Unsupported algorithm");
+}
+
+#[test]
+fn fail_provisioning_uri_with_otp_length_less_than_6() {
+    let hotp_tool = HOTP::new(Algorithm::SHA512, SECRET, 4, 10).unwrap();
+
+    let result = hotp_tool.provisioning_uri("test", 0);
+
+    assert!(result.is_err(), "Expected an error");
+    assert_eq!(result.err().unwrap(), "OTP length must be 6");
+}
+
+#[test]
+fn fail_provisioning_uri_with_otp_length_more_than_6() {
+    let hotp_tool = HOTP::new(Algorithm::SHA512, SECRET, 8, 10).unwrap();
+
+    let result = hotp_tool.provisioning_uri("test", 0);
+
+    assert!(result.is_err(), "Expected an error");
+    assert_eq!(result.err().unwrap(), "OTP length must be 6");
+}
+
+#[test]
+fn fail_provisioning_uri_with_radix_less_than_10() {
+    let hotp_tool = HOTP::new(Algorithm::SHA512, SECRET, 6, 9).unwrap();
+
+    let result = hotp_tool.provisioning_uri("test", 0);
+
+    assert!(result.is_err(), "Expected an error");
+    assert_eq!(result.err().unwrap(), "Radix must be 10");
+}
+
+#[test]
+fn fail_provisioning_uri_with_radix_more_than_10() {
+    let hotp_tool = HOTP::new(Algorithm::SHA512, SECRET, 6, 11).unwrap();
+
+    let result = hotp_tool.provisioning_uri("test", 0);
+
+    assert!(result.is_err(), "Expected an error");
+    assert_eq!(result.err().unwrap(), "Radix must be 10");
+}