Although it will depend on the implementation details of your particular case, the general approach will be to start a server (in a separate goroutine, as you already hinted), and listen to the incoming connections.
For example, let's spin up a server and verify that the content we are reading from the connection is indeed the one we send over from the client:
func TestConn(t *testing.T) {
message := "Hi there!
"
go func() {
conn, err := net.Dial("tcp", ":3000")
if err != nil {
t.Fatal(err)
}
defer conn.Close()
if _, err := fmt.Fprintf(conn, message); err != nil {
t.Fatal(err)
}
}()
l, err := net.Listen("tcp", ":3000")
if err != nil {
t.Fatal(err)
}
defer l.Close()
for {
conn, err := l.Accept()
if err != nil {
return
}
defer conn.Close()
buf, err := ioutil.ReadAll(conn)
if err != nil {
t.Fatal(err)
}
fmt.Println(string(buf[:]))
if msg := string(buf[:]); msg != message {
t.Fatalf("Unexpected message:
Got:\t\t%s
Expected:\t%s
", msg, message)
}
return // Done
}
}
Note that here I'm not starting the server in the goroutine, as otherwise the test case is likely to be finished before the listener has run the test.