add shutdown context unit test

cmd/api_serve.go

@@ -65,6 +65,7 @@ func aptlyAPIServe(cmd *commander.Command, args []string) error {
 	signal.Notify(sigchan, syscall.SIGINT, syscall.SIGTERM)
 	go (func() {
 		if _, ok := <-sigchan; ok {
+			fmt.Printf("\nShutdown signal received, waiting for background tasks...\n")
 			context.TaskList().Wait()
 			server.Shutdown(stdcontext.Background())
 		}

http/download_test.go

@@ -154,3 +154,13 @@ func (s *DownloaderSuite) TestGetLengthConnectError(c *C) {
 
 	c.Assert(err, ErrorMatches, ".*no such host")
 }
+
+func (s *DownloaderSuite) TestContextCancel(c *C) {
+	ctx, cancel := context.WithCancel(s.ctx)
+	s.ctx = ctx
+
+	cancel()
+	_, err := s.d.GetLength(s.ctx, "http://nosuch.host.invalid./")
+
+	c.Assert(err, ErrorMatches, ".*context canceled.*")
+}