test: racy port creation in port forwarding tests (testcontainers#2688)

* test: racy port creation in port forwarding tests

Fix racy creation of free ports in port forwarding tests which were
causing random failures.

* chore: apply feedback suggestions

Apply PR feedback suggestions to use a single line error check.

Co-authored-by: Manuel de la Peña <social.mdelapenya@gmail.com>

---------

Co-authored-by: Manuel de la Peña <social.mdelapenya@gmail.com>

port_forwarding_test.go

@@ -6,9 +6,12 @@ import (
 	"io"
 	"net"
 	"net/http"
+	"net/http/httptest"
 	"testing"
 	"time"
 
+	"github.com/stretchr/testify/require"
+
 	"github.com/testcontainers/testcontainers-go"
 	tcexec "github.com/testcontainers/testcontainers-go/exec"
 	"github.com/testcontainers/testcontainers-go/network"
@@ -52,21 +55,10 @@ func TestExposeHostPorts(t *testing.T) {
 		t.Run(tc.name, func(tt *testing.T) {
 			freePorts := make([]int, tc.numberOfPorts)
 			for i := range freePorts {
-				freePort, err := getFreePort()
-				if err != nil {
-					tt.Fatal(err)
-				}
-
-				freePorts[i] = freePort
-
-				// create an http server for each port
-				server, err := createHttpServer(freePort)
-				if err != nil {
-					tt.Fatal(err)
-				}
-				go func() {
-					_ = server.ListenAndServe()
-				}()
+				server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+					fmt.Fprint(w, expectedResponse)
+				}))
+				freePorts[i] = server.Listener.Addr().(*net.TCPAddr).Port
 				tt.Cleanup(func() {
 					server.Close()
 				})
@@ -87,13 +79,10 @@ func TestExposeHostPorts(t *testing.T) {
 			if tc.hasNetwork {
 				var err error
 				nw, err = network.New(context.Background())
-				if err != nil {
-					tt.Fatal(err)
-				}
+				require.NoError(tt, err)
+
 				tt.Cleanup(func() {
-					if err := nw.Remove(context.Background()); err != nil {
-						tt.Fatal(err)
-					}
+					require.NoError(tt, nw.Remove(context.Background()))
 				})
 
 				req.Networks = []string{nw.Name}
@@ -108,13 +97,9 @@ func TestExposeHostPorts(t *testing.T) {
 			}
 
 			c, err := testcontainers.GenericContainer(ctx, req)
-			if err != nil {
-				tt.Fatal(err)
-			}
+			require.NoError(tt, err)
 			tt.Cleanup(func() {
-				if err := c.Terminate(context.Background()); err != nil {
-					tt.Fatal(err)
-				}
+				require.NoError(tt, c.Terminate(context.Background()))
 			})
 
 			if tc.hasHostAccess {
@@ -174,30 +159,3 @@ func assertContainerHasNoHostAccess(t *testing.T, c testcontainers.Container, po
 		}
 	}
 }
-
-func createHttpServer(port int) (*http.Server, error) {
-	server := &http.Server{
-		Addr: fmt.Sprintf(":%d", port),
-	}
-
-	server.Handler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		fmt.Fprint(w, expectedResponse)
-	})
-
-	return server, nil
-}
-
-// getFreePort asks the kernel for a free open port that is ready to use.
-func getFreePort() (int, error) {
-	addr, err := net.ResolveTCPAddr("tcp", "localhost:0")
-	if err != nil {
-		return 0, err
-	}
-
-	l, err := net.ListenTCP("tcp", addr)
-	if err != nil {
-		return 0, err
-	}
-	defer l.Close()
-	return l.Addr().(*net.TCPAddr).Port, nil
-}