diff --git a/src/server.py b/src/server.py
index c53f100..add9be8 100755
--- a/src/server.py
+++ b/src/server.py
@@ -22,15 +22,14 @@ class RequestHandler(socketserver.BaseRequestHandler):
 
     def command_nickname(self, user, desired_nickname):
 
-        if desired_nickname not in self.user_list:
-            self.user_list.append(desired_nickname)
-            self.user_list.remove(user)
-            message = ":" + user + " NICK " + desired_nickname
+        if desired_nickname not in self.user_dict.keys():
+            self.user_dict[desired_nickname] = dict()
+            self.user_dict.pop(user)
             return True
         else:
-            self.user_list.remove(desired_nickname)
-            if user in self.user_list:
-                self.user_list.remove(user)
+            self.user_dict.pop(desired_nickname)
+            if user in self.user_dict:
+                self.user_dict.pop(user)
             # issue kill command (?)
             return True
 
diff --git a/test/test_server.py b/test/test_server.py
index 2726049..4cacb74 100644
--- a/test/test_server.py
+++ b/test/test_server.py
@@ -14,72 +14,29 @@ def test_ping(server):
 
 @pytest.mark.parametrize("test_input,expected", [("password", True), ("wrong password", False)])
 def test_command_pass(server, test_input, expected):
-    """
-           Command: PASS
-    Parameters: <password>
-
-    The PASS command is used to set a 'connection password'.  The
-    password can and must be set before any attempt to register the
-    connection is made.  Currently this requires that clients send a PASS
-    command before sending the NICK/USER combination and servers *must*
-    send a PASS command before any SERVER command.  The password supplied
-    must match the one contained in the C/N lines (for servers) or I
-    lines (for clients).  It is possible to send multiple PASS commands
-    before registering but only the last one sent is used for
-    verification and it may not be changed once registered.  Numeric
-    Replies:
-
-           ERR_NEEDMOREPARAMS              ERR_ALREADYREGISTRED
-
-    Example:
-
-           PASS secretpasswordhere
-    """
     server.password = "password"
     assert server.command_pass(server, test_input) == expected
 
 
-def create_user_list():
-    user_list = list()
+def create_user_dict():
+    user_dict = dict()
     user_id = "user"
     for i in range(0, 9):
-        user_list.append((user_id + str(i)))
+        user_dict[(user_id + str(i))] = dict()
 
-    return user_list
+    return user_dict
 
 
-@pytest.mark.parametrize("user_list, user_to_change, nickname, expected_result",
+@pytest.mark.parametrize("user_dict, user_to_change, nickname, expected_result",
                          [
-                             (create_user_list(), "user2", "wayne", True),
-                             (create_user_list(), "user2", "user4", True),
-                             (create_user_list(), "user2", "christoph", True),
-                             (create_user_list(), "user2", "user19", True)])
-def test_change_nickname(server, user_list,user_to_change, nickname, expected_result):
-    """
-        Command: NICK
-       Parameters: <nickname> [ <hopcount> ]
-
-       NICK message is used to give user a nickname or change the previous
-       one.  The <hopcount> parameter is only used by servers to indicate
-       how far away a nick is from its home server.  A local connection has
-       a hopcount of 0.  If supplied by a client, it must be ignored.
-
-       If a NICK message arrives at a server which already knows about an
-       identical nickname for another client, a nickname collision occurs.
-       As a result of a nickname collision, all instances of the nickname
-       are removed from the server's database, and a KILL command is issued
-       to remove the nickname from all other server's database. If the NICK
-       message causing the collision was a nickname change, then the
-       original (old) nick must be removed as well.
-
-       If the server recieves an identical NICK from a client which is
-       directly connected, it may issue an ERR_NICKCOLLISION to the local
-       client, drop the NICK command, and not generate any kills.
-    """
-    server.user_list = create_user_list()
+                             (create_user_dict(), "user2", "wayne", True),
+                             (create_user_dict(), "user2", "user4", True),
+                             (create_user_dict(), "user2", "christoph", True),
+                             (create_user_dict(), "user2", "user19", True),
+                             ({"WiZ": {}}, "WiZ", "Kilroy", True)])
+def test_change_nickname(server, user_dict, user_to_change, nickname, expected_result):
+    server.user_dict = user_dict.copy()
     assert server.command_nickname(server, user_to_change, nickname) == expected_result
-    assert user_to_change not in server.user_list
-    if nickname not in user_list:
-        assert nickname in server.user_list
-    else:
-        assert nickname not in server.user_list
+    assert user_to_change not in server.user_dict
+    if nickname in user_dict:
+        assert nickname not in server.user_dict, nickname + " should have been deleted due to name collision"