diff --git a/src/message/encoder.rs b/src/message/encoder.rs
index ab9ec99..5e47d45 100644
--- a/src/message/encoder.rs
+++ b/src/message/encoder.rs
@@ -143,7 +143,7 @@ mod test {
         let mut c = SevenBitCodec::new();
 
         assert_eq!(
-            &String::from_utf8(c.encode("Hello, world!".as_bytes())).unwrap(),
+            &String::from_utf8(c.encode(b"Hello, world!")).unwrap(),
             "Hello, world!"
         );
     }
@@ -212,10 +212,7 @@ mod test {
     fn base64_encodeed() {
         let mut c = Base64Codec::new();
 
-        assert_eq!(
-            &String::from_utf8(c.encode("Chunk.".as_bytes())).unwrap(),
-            "Q2h1bmsu"
-        );
+        assert_eq!(&String::from_utf8(c.encode(b"Chunk.")).unwrap(), "Q2h1bmsu");
     }
 
     #[test]
@@ -223,7 +220,7 @@ mod test {
         let mut c = EightBitCodec::new();
 
         assert_eq!(
-            &String::from_utf8(c.encode("Hello, world!".as_bytes())).unwrap(),
+            &String::from_utf8(c.encode(b"Hello, world!")).unwrap(),
             "Hello, world!"
         );
 
@@ -238,7 +235,7 @@ mod test {
         let mut c = BinaryCodec::new();
 
         assert_eq!(
-            &String::from_utf8(c.encode("Hello, world!".as_bytes())).unwrap(),
+            &String::from_utf8(c.encode(b"Hello, world!")).unwrap(),
             "Hello, world!"
         );
 
diff --git a/src/message/mimebody.rs b/src/message/mimebody.rs
index 340cb46..a189a14 100644
--- a/src/message/mimebody.rs
+++ b/src/message/mimebody.rs
@@ -535,7 +535,7 @@ mod test {
                         parameters: vec![header::DispositionParam::Filename(
                             header::Charset::Ext("utf-8".into()),
                             None,
-                            "example.c".as_bytes().into(),
+                            "example.c".into(),
                         )],
                     })
                     .header(header::ContentTransferEncoding::Binary)
@@ -582,7 +582,7 @@ mod test {
                         parameters: vec![header::DispositionParam::Filename(
                             header::Charset::Ext("utf-8".into()),
                             None,
-                            "encrypted.asc".as_bytes().into(),
+                            "encrypted.asc".into(),
                         )],
                     })
                     .body(String::from(concat!(
@@ -637,7 +637,7 @@ mod test {
                     parameters: vec![header::DispositionParam::Filename(
                         header::Charset::Ext("utf-8".into()),
                         None,
-                        "signature.asc".as_bytes().into(),
+                        "signature.asc".into(),
                     )],
                 })
                 .body(String::from(concat!(
@@ -725,7 +725,7 @@ mod test {
                              .header(header::ContentType("text/plain; charset=utf8".parse().unwrap()))
                              .header(header::ContentDisposition {
                                  disposition: header::DispositionType::Attachment,
-                                 parameters: vec![header::DispositionParam::Filename(header::Charset::Ext("utf-8".into()), None, "example.c".as_bytes().into())]
+                                 parameters: vec![header::DispositionParam::Filename(header::Charset::Ext("utf-8".into()), None, "example.c".into())]
                              })
                              .header(header::ContentTransferEncoding::Binary)
                              .body(String::from("int main() { return 0; }")));
diff --git a/src/transport/smtp/commands.rs b/src/transport/smtp/commands.rs
index 3666430..08b9844 100644
--- a/src/transport/smtp/commands.rs
+++ b/src/transport/smtp/commands.rs
@@ -335,7 +335,7 @@ mod test {
             "RCPT TO:<test@example.com>\r\n"
         );
         assert_eq!(
-            format!("{}", Rcpt::new(email.clone(), vec![rcpt_parameter])),
+            format!("{}", Rcpt::new(email, vec![rcpt_parameter])),
             "RCPT TO:<test@example.com> TEST=value\r\n"
         );
         assert_eq!(format!("{}", Quit), "QUIT\r\n");
@@ -366,7 +366,7 @@ mod test {
         assert_eq!(
             format!(
                 "{}",
-                Auth::new(Mechanism::Login, credentials.clone(), None).unwrap()
+                Auth::new(Mechanism::Login, credentials, None).unwrap()
             ),
             "AUTH LOGIN\r\n"
         );
diff --git a/src/transport/smtp/extension.rs b/src/transport/smtp/extension.rs
index 42527e2..e684465 100644
--- a/src/transport/smtp/extension.rs
+++ b/src/transport/smtp/extension.rs
@@ -320,7 +320,7 @@ mod test {
                 "{}",
                 ServerInfo {
                     name: "name".to_string(),
-                    features: eightbitmime.clone(),
+                    features: eightbitmime,
                 }
             ),
             "name with {EightBitMime}".to_string()
@@ -347,7 +347,7 @@ mod test {
                 "{}",
                 ServerInfo {
                     name: "name".to_string(),
-                    features: plain.clone(),
+                    features: plain,
                 }
             ),
             "name with {Authentication(Plain)}".to_string()