diff --git a/Readme.md b/Readme.md
index 7a2f74b..d67fe77 100644
--- a/Readme.md
+++ b/Readme.md
@@ -15,3 +15,27 @@ you will find the result in `./target/release`
 If you want to build the `Hati` server, you don't need to build this library
 separately. Just build the server and it will automatically include this lib
 
+# Developing
+
+we recommend to use the nix environment, so that you will have
+exactly the same environment as the developers.
+
+just enter the repository directory and run
+
+```
+nix develop
+```
+
+and everything should be done for you.
+
+## Git
+
+Please configure a pre-commit hook like the one in `var/git-pre-commit`
+
+```
+cp var/git-pre-commit .git/hooks/pre-commit
+```
+
+This will run `cargo test --offline` right before your commit,
+to make sure that everything compiles and that the test pass
+
diff --git a/src/connection/handshake/tests.rs b/src/connection/handshake/tests.rs
index 9530407..c5f84dd 100644
--- a/src/connection/handshake/tests.rs
+++ b/src/connection/handshake/tests.rs
@@ -8,11 +8,7 @@ use crate::{
 fn test_handshake_dirsync_req() {
     let rand = enc::Random::new();
     let secret = enc::Secret::new_rand(&rand);
-    let cipher_send = enc::sym::CipherSend::new(
-        enc::sym::CipherKind::XChaCha20Poly1305,
-        secret,
-        &rand,
-    );
+    let cipher = enc::sym::CipherKind::XChaCha20Poly1305;
 
     let (_, exchange_key) =
         match enc::asym::KeyExchangeKind::X25519DiffieHellman.new_keypair(&rand)
@@ -49,11 +45,7 @@ fn test_handshake_dirsync_req() {
 
     let mut bytes = Vec::<u8>::with_capacity(h_req.len());
     bytes.resize(h_req.len(), 0);
-    h_req.serialize(
-        cipher_send.kind().nonce_len(),
-        cipher_send.kind().tag_len(),
-        &mut bytes,
-    );
+    h_req.serialize(cipher.nonce_len(), cipher.tag_len(), &mut bytes);
 
     let mut deserialized = match Handshake::deserialize(&bytes) {
         Ok(deserialized) => deserialized,
@@ -65,10 +57,9 @@ fn test_handshake_dirsync_req() {
     if let HandshakeData::DirSync(dirsync::DirSync::Req(r_a)) =
         &mut deserialized.data
     {
-        let enc_start =
-            r_a.encrypted_offset() + cipher_send.kind().nonce_len().0;
+        let enc_start = r_a.encrypted_offset() + cipher.nonce_len().0;
         if let Err(e) = r_a.data.deserialize_as_cleartext(
-            &bytes[enc_start..(bytes.len() - cipher_send.kind().tag_len().0)],
+            &bytes[enc_start..(bytes.len() - cipher.tag_len().0)],
         ) {
             assert!(false, "DirSync Req Inner serialize: {}", e.to_string());
         }
diff --git a/var/git-pre-commit b/var/git-pre-commit
new file mode 100755
index 0000000..81ac843
--- /dev/null
+++ b/var/git-pre-commit
@@ -0,0 +1,4 @@
+#!/usr/bin/env bash
+
+RUSTFLAGS=-Awarnings exec cargo test --offline --profile dev
+