Adding instructions for unittesting

CONTRIBUTING.md

@@ -22,6 +22,79 @@ a pull request, or ask some of your friends to do so.
 are watching the issue tracker here, you'll probably get no help from here.
 Read [Troubleshooting] and get help from forums or [mailing lists].
 
+How To Run Unittests Locally
+----
+
+Since `ss` is written in python, you probably can develop it on your own
+favorate platform. The following instructions are based on debian wheezy.
+
+### Prerequisites
+
+1. Debian packages
+
+        # apt-get install python-pip swig libssl-dev python-dev curl
+
+2. Python packages
+
+        # pip install coverage pep8 pyflakes nose M2Crypto numpy salsa20
+
+3. libsodium and socksify
+
+   You must issue the `install.sh` for `socksify` from your local repo root:
+
+        # pwd
+        /path/to/your/shadowsocks
+
+   Run the script:
+
+        # tests/socksify/install.sh
+
+   The `install.sh` for `libsodium` is location free. 
+   To be simple, we invoke it from the same location:
+
+        # tests/libsodium/install.sh
+
+### Running unittests
+
+You must issue it from your local repo root:
+
+    $ pwd
+    /path/to/your/shadowsocks
+
+The command is `.jenkins.sh`. Invoke like this:
+
+    $ ./.jenkins.sh
+
+Note that we are running `.jenkins.sh` as normal user.
+
+Be aware that `.jenkins.sh` does not stop when the first failure occurs. 
+Instead, it runs through all tests and reports all failures.
+
+### Special tests
+
+* For me, the following test in `.jenkins.sh` does not get passed by default:
+
+          run_test python tests/test.py --with-coverage -c tests/table.json
+
+  I have to modify `tests/test.py:104`
+
+        time.sleep(2)
+
+  and increase the delay.
+
+* `tests/test_large_file.sh` requires an http server to host a downloadable
+file at http://127.0.0.1/file . If you do not have a local httpd server running,
+  here is an easy way to do that:
+
+      # pwd
+      /path/to/your/shadowsocks
+      # echo "TEST" > file
+      # python -m SimpleHTTPServer 80
+
+  Note that to bind SimpleHTTPServer to `80`, you need super user privilege.
+Alternatively, you can modify `tests/test_large_file.sh` to use a different
+port.
 
 [Troubleshooting]: https://github.com/clowwindy/shadowsocks/wiki/Troubleshooting
 [mailing lists]:   https://groups.google.com/forum/#!forum/shadowsocks
+