net/imap: Net::IMAP#disconnect need not do anything if already disconnected

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58663 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/net/imap.rb

@@ -325,6 +325,7 @@ module Net
 
     # Disconnects from the server.
     def disconnect
+      return if disconnected?
       begin
         begin
           # try to call SSL::SSLSocket#io.

test/net/imap/test_imap.rb

@@ -526,6 +526,33 @@ class IMAPTest < Test::Unit::TestCase
     end
   end
 
+  def test_disconnect
+    server = create_tcp_server
+    port = server.addr[1]
+    @threads << Thread.start do
+      sock = server.accept
+      begin
+        sock.print("* OK test server\r\n")
+        sock.gets
+        sock.print("* BYE terminating connection\r\n")
+        sock.print("RUBY0001 OK LOGOUT completed\r\n")
+      ensure
+        sock.close
+        server.close
+      end
+    end
+    begin
+      imap = Net::IMAP.new(SERVER_ADDR, :port => port)
+      imap.logout
+      imap.disconnect
+      assert_equal(true, imap.disconnected?)
+      imap.disconnect
+      assert_equal(true, imap.disconnected?)
+    ensure
+      imap.disconnect if imap && !imap.disconnected?
+    end
+  end
+
   private
 
   def imaps_test