use fake for auth adapter test

Author: jch

test/test_auth_adapter.rb

@@ -1,9 +1,14 @@
 require 'test_helper'
 
 class TestAuthAdapter < Test::Unit::TestCase
+  class FakeSocket
+    def initialize(*args)
+    end
+  end
+
   def test_undefined_auth_adapter
-    flexmock(TCPSocket).should_receive(:new).ordered.with('ldap.example.com', 379).once.and_return(nil)
     conn = Net::LDAP::Connection.new(host: 'ldap.example.com', port: 379)
+    conn.socket_class = FakeSocket
     assert_raise Net::LDAP::AuthMethodUnsupportedError, "Unsupported auth method (foo)" do
       conn.bind(method: :foo)
     end