diff --git a/src/proto/codec.rs b/src/proto/codec.rs
index 2b910d9..eed20b8 100644
--- a/src/proto/codec.rs
+++ b/src/proto/codec.rs
@@ -338,9 +338,10 @@ impl<T: ProtoEncode> ProtoEncode for Vec<T> {
  *=======*/
 
 #[cfg(test)]
-mod tests {
+pub mod tests {
     use super::{ProtoDecoder, ProtoEncoder, ProtoDecode, ProtoEncode};
 
+    use std::fmt;
     use std::io;
     use std::net;
     use std::u16;
@@ -348,6 +349,16 @@ mod tests {
 
     use bytes::{Buf, BytesMut};
 
+    pub fn roundtrip<T: fmt::Debug + Eq + PartialEq + ProtoDecode + ProtoEncode>(input: T) {
+        let mut bytes = BytesMut::new();
+        input.encode(&mut ProtoEncoder::new(&mut bytes)).unwrap();
+
+        let mut cursor = io::Cursor::new(bytes);
+        let output = T::decode(&mut ProtoDecoder::new(&mut cursor)).unwrap();
+
+        assert_eq!(output, input);
+    }
+
     // Helper for succinctness in tests below.
     fn new_cursor(vec: Vec<u8>) -> io::Cursor<BytesMut> {
         io::Cursor::new(BytesMut::from(vec))
@@ -387,6 +398,13 @@ mod tests {
         }
     }
 
+    #[test]
+    fn roundtrip_u32() {
+        for &(val, _) in &U32_ENCODINGS {
+            roundtrip(val)
+        }
+    }
+
     #[test]
     fn encode_bool() {
         let mut bytes = BytesMut::from(vec![13]);
@@ -418,6 +436,12 @@ mod tests {
         ProtoDecoder::new(&mut cursor).decode_bool().unwrap();
     }
 
+    #[test]
+    fn roundtrip_bool() {
+        roundtrip(false);
+        roundtrip(true);
+    }
+
     #[test]
     fn encode_u16() {
         for &(val, ref encoded_bytes) in &U32_ENCODINGS {
@@ -450,6 +474,22 @@ mod tests {
         }
     }
 
+    #[test]
+    #[should_panic]
+    fn decode_u16_invalid() {
+        let mut cursor = new_cursor(vec![0, 0, 1, 0]);
+        ProtoDecoder::new(&mut cursor).decode_u16().unwrap();
+    }
+
+    #[test]
+    fn roundtrip_u16() {
+        for &(val, _) in &U32_ENCODINGS {
+            if val <= u16::MAX as u32 {
+                roundtrip(val)
+            }
+        }
+    }
+
     #[test]
     fn encode_ipv4() {
         for &(val, ref encoded_bytes) in &U32_ENCODINGS {
@@ -475,6 +515,13 @@ mod tests {
         }
     }
 
+    #[test]
+    fn roundtrip_ipv4() {
+        for &(val, _) in &U32_ENCODINGS {
+            roundtrip(net::Ipv4Addr::from(val))
+        }
+    }
+
     // A few strings and their corresponding encodings.
     const STRING_ENCODINGS: [(&'static str, &'static [u8]); 3] =
         [
@@ -515,6 +562,13 @@ mod tests {
         }
     }
 
+    #[test]
+    fn roundtrip_string() {
+        for &(string, _) in &STRING_ENCODINGS {
+            roundtrip(string.to_string())
+        }
+    }
+
     #[test]
     fn encode_u32_vector() {
         let mut vec = vec![];
@@ -545,4 +599,9 @@ mod tests {
         assert_eq!(vec, expected_vec);
         assert_eq!(cursor.remaining(), 0);
     }
+
+    #[test]
+    fn roundtrip_u32_vector() {
+        roundtrip(vec![0u32, 1, 2, 3, 4, 5, 6, 7, 8, 9])
+    }
 }
diff --git a/src/proto/peer/message.rs b/src/proto/peer/message.rs
index 5452c6f..632821d 100644
--- a/src/proto/peer/message.rs
+++ b/src/proto/peer/message.rs
@@ -155,19 +155,10 @@ mod tests {
     use bytes::BytesMut;
 
     use proto::{DecodeError, ProtoDecode, ProtoDecoder, ProtoEncode, ProtoEncoder};
+    use proto::codec::tests::roundtrip;
 
     use super::*;
 
-    fn roundtrip(input: Message) {
-        let mut bytes = BytesMut::new();
-        input.encode(&mut ProtoEncoder::new(&mut bytes)).unwrap();
-
-        let mut cursor = io::Cursor::new(bytes);
-        let output = Message::decode(&mut ProtoDecoder::new(&mut cursor)).unwrap();
-
-        assert_eq!(output, input);
-    }
-
     #[test]
     fn invalid_code() {
         let mut bytes = BytesMut::new();
diff --git a/src/proto/server/request.rs b/src/proto/server/request.rs
index 27e8f75..f37dd74 100644
--- a/src/proto/server/request.rs
+++ b/src/proto/server/request.rs
@@ -590,19 +590,10 @@ mod tests {
     use bytes::BytesMut;
 
     use proto::{DecodeError, ProtoDecode, ProtoDecoder, ProtoEncode, ProtoEncoder};
+    use proto::codec::tests::roundtrip;
 
     use super::*;
 
-    fn roundtrip(input: ServerRequest) {
-        let mut bytes = BytesMut::new();
-        input.encode(&mut ProtoEncoder::new(&mut bytes)).unwrap();
-
-        let mut cursor = io::Cursor::new(bytes);
-        let output = ServerRequest::decode(&mut ProtoDecoder::new(&mut cursor)).unwrap();
-
-        assert_eq!(output, input);
-    }
-
     #[test]
     fn invalid_code() {
         let mut bytes = BytesMut::new();