fix: eliminate port race in setupFakeEnvoyStats test helper

net.Listen(":0") followed by l.Close() and a later ListenAndServe() on
the resulting port number leaves a window where another process (or a
concurrently running test) can grab that exact ephemeral port before
the re-bind happens, causing TestGetTotalConnections to fail with
connection errors on loaded machines. Serve on the already-bound
listener directly via s.Serve(l) so the port is never released.

Signed-off-by: Muhammad Waqar <mwaqar@confluent.io>

Author: muwaqar-cflt

internal/cmd/envoy/shutdown_manager_test.go

@@ -21,9 +21,9 @@ import (
 
 // setupFakeEnvoyStats set up an HTTP server return content
 func setupFakeEnvoyStats(t *testing.T, content string) *http.Server {
+	// Reuse the bound listener instead of closing and re-binding the port.
 	l, err := net.Listen("tcp", ":0") //nolint: gosec
 	require.NoError(t, err)
-	require.NoError(t, l.Close())
 	mux := http.NewServeMux()
 	mux.HandleFunc("/", func(writer http.ResponseWriter, _ *http.Request) {
 		writer.Header().Set("Content-Type", "application/json")
@@ -39,7 +39,7 @@ func setupFakeEnvoyStats(t *testing.T, content string) *http.Server {
 	}
 	t.Logf("start to listen at %s ", addr)
 	go func() {
-		if err := s.ListenAndServe(); err != nil {
+		if err := s.Serve(l); err != nil {
 			fmt.Println("fail to listen: ", err)
 		}
 	}()