basic 005 parameter validation test (#255)

* basic 005 parameter validation test

The overall order of the registration burst is covered by
ConnectionRegistrationTestCase.testConnectionRegistration and doesn't need
to be checked here.

* Update irctest/server_tests/isupport.py

Co-authored-by: Val Lorentz <progval+github@progval.net>

---------

Co-authored-by: Val Lorentz <progval+github@progval.net>

irctest/server_tests/isupport.py

@@ -9,6 +9,38 @@ from irctest import cases, runner
 
 
 class IsupportTestCase(cases.BaseServerTestCase):
+    @cases.mark_specifications("Modern")
+    @cases.mark_isupport("PREFIX")
+    def testParameters(self):
+        """https://modern.ircdocs.horse/#rplisupport-005"""
+
+        # <https://modern.ircdocs.horse/#connection-registration>
+        # "Upon successful completion of the registration process,
+        #  the server MUST send, in this order:
+        #  [...]
+        #  5. at least one RPL_ISUPPORT (005) numeric to the client."
+        welcome_005s = [
+            msg for msg in self.connectClient("foo") if msg.command == "005"
+        ]
+        self.assertGreaterEqual(len(welcome_005s), 1)
+        for msg in welcome_005s:
+            # first parameter is the client's nickname;
+            # last parameter is a human-readable trailing, typically
+            # "are supported by this server"
+            self.assertGreaterEqual(len(msg.params), 3)
+            self.assertEqual(msg.params[0], "foo")
+            # "As the maximum number of message parameters to any reply is 15,
+            # the maximum number of RPL_ISUPPORT tokens that can be advertised
+            # is 13."
+            self.assertLessEqual(len(msg.params), 15)
+            for param in msg.params[1:-1]:
+                self.validateIsupportParam(param)
+
+    def validateIsupportParam(self, param):
+        if not param.isascii():
+            raise ValueError("Invalid non-ASCII 005 parameter", param)
+        # TODO add more validation
+
     @cases.mark_specifications("Modern")
     @cases.mark_isupport("PREFIX")
     def testPrefix(self):