How does one test net.Conn in unit tests in Golang?

I’m currently looking into creating some unit tests for net.Conn interface in Go, as well as other functions that build up on top of that functionality, and I’m wondering what is the best way to unit test that in Google Go? My code looks like:

conn, _:=net.Dial("tcp", "127.0.0.1:8080")
...
fmt.Fprintf(conn, "test")
...
buffer:=make([]byte, 100)
conn.Read(buffer)

Is the most efficient way of testing this code and the code that uses these functions to spin up a separate goroutine to act like the server, use net.http.httptest package, or something else?

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!\n"

    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:\nGot:\t\t%s\nExpected:\t%s\n", 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.