"Connection refused" error in a flaky unit test which involves starting an HTTP server and connecting to it

I'm trying to debug a flaky unit test which is similar to the following:

package main

import (
	"net"
	"net/http"
	"testing"
	"time"

	"github.com/stretchr/testify/require"
)

func TestFlaky(t *testing.T) {
	// Mock an API
	http.HandleFunc("/foo/bar", func(w http.ResponseWriter, r *http.Request) {
		_, err := w.Write([]byte("foobar"))
		require.NoError(t, err)
	})
	go func() {
		require.NoError(t, http.ListenAndServe("localhost:7777", nil))
	}()

	// Wait (up to 1 second) for the mocked API to be available
	conn, err := net.DialTimeout("tcp", "localhost:7777", time.Second)
	require.NoError(t, err)
	require.NoError(t, conn.Close())
}

However, from the require.NoError() line right after the DialTimeout error, I'm getting the following error (in a CI environment only):

     --- FAIL: TestFlaky (0.00s)
         main_test.go:24: 
             	Error Trace:	main_test.go:24
             	Error:      	Received unexpected error:
             	            	dial tcp [::1]:7777: connect: connection refused
             	Test:       	TestFlaky

Since the test fails immediately, I'm guessing this is not a matter of adjusting the timeout. How should I make this test non-flaky? I'm considering replacing the last three lines with a require.Eventually similar to the following:

	var conn net.Conn
	require.Eventually(t, func() bool {
		var err error
		conn, err = net.DialTimeout("tcp", "localhost:7777", time.Second)
		if err != nil {
			t.Logf("DialTimeout error: %v. Retrying...", err)
			return false
		}
		return true
	}, time.Second, 100*time.Millisecond)
	require.NoError(t, conn.Close())

Would this suffice to remove test flakiness?

The code inside the goroutine does not guarantee to be executed before the Dial. (If you put a sleep just after the goroutine it should work but it is an ugly solution).

Also, notice that "dial with timeout" is waiting for tcp packets when connection is being stablished, but the refused connection is actually the RST packet.

Hint: see how httptest package works.

Edit: here is how httptest works: https://cs.opensource.google/go/go/+/refs/tags/go1.16.6:src/net/http/httptest/server.go;l=304

func (s *Server) goServe() {
	s.wg.Add(1)
	go func() {
		defer s.wg.Done()
		s.Config.Serve(s.Listener)
	}()
}