Finally fixed CI test

main_test.go

@@ -1,7 +1,7 @@
 package main
 
 import (
-	"net/http"
+	"net"
 	"os"
 	"testing"
 	"time"
@@ -14,9 +14,10 @@ func TestInitShortener(t *testing.T) {
 	if err != nil {
 		t.Fatalf("could not init shortener: %v", err)
 	}
-	time.Sleep(1) // Give the http server a second to boot up
-	if err := http.ListenAndServe(viper.GetString("listen_addr"), nil); err == nil {
-		t.Fatal("port is not in use")
+	time.Sleep(time.Second) // Give the http server a second to boot up
+	// We expect there a port is in use error
+	if _, err := net.Listen("tcp", viper.GetString("listen_addr")); err == nil {
+		t.Fatalf("port is not in use: %v", err)
 	}
 	close()
 	os.Exit(0)