Proper way to test a connection in go - unit-testing

Question

I am covering project with tests and for that purpose I need dummy TCP Server, which could accept connection, write/read data to/from it, close it etc... I have found this question on stack overflow, covering mocking connection, but it doesn't cover what I actually need to test.
My idea relies on this article as starting point, but when I started implementing channel to let server write some data to newly opened connection, I got stuck with undebuggable deadlock in writing to channel.
What I want to achieve is to write some data to server's channel, say sendingQueue chan *[]byte, so later corresponding []byte will be sent to newly established connection.
During these little research I have tried debugging and printing out messages before/after sending data to channel and trying to send / read data from channel in different places of program.
What I found out:
My idea works if I add data directly in handleConnection with
go func() {
f := []byte("test.")
t.sendingQueue <- &f
}()
My idea doesn't work if I push data to channel from TestUtils_TestingTCPServer_WritesRequest in any form, either with func (t *TCPServer) Put(data *[]byte) (err error) or directly with:
go func(queue chan *[]byte, data *[]byte) {
queue <- data
}(t.sendingQueue, &payload)
It doesn't matter if channel is buffered or not.
So, obviously, there is something wrong either with the way I debug my code (I didn't dive into cli dlv, using just IDE debugger), or something that I completely miss about working with go channels, goroutines or net.Conn module.
For convenience public gist with full code is available. Note — there is // INIT part in the TestUtils_TestingTCPServer_WritesRequest which is required to run/debug single test. It should be commented out when running go test in the directory.
utils.go:
// NewServer creates a new Server using given protocol
// and addr.
func NewTestingTCPServer(protocol, addr string) (*TCPServer, error) {
switch strings.ToLower(protocol) {
case "tcp":
return &TCPServer{
addr: addr,
sendingQueue: make(chan *[]byte, 10),
}, nil
case "udp":
}
return nil, errors.New("invalid protocol given")
}
// TCPServer holds the structure of our TCP
// implementation.
type TCPServer struct {
addr string
server net.Listener
sendingQueue chan *[]byte
}
func (t *TCPServer) Run() (err error) {}
func (t *TCPServer) Close() (err error) {}
func (t *TCPServer) Put(data *[]byte) (err error) {}
func (t *TCPServer) handleConnection(conn net.Conn){
// <...>
// Putting data here successfully sends it via freshly established
// Connection:
// go func() {
// f := []byte("test.")
// t.sendingQueue <- &f
// }()
for {
fmt.Printf("Started for loop\n")
select {
case data := <-readerChannel:
fmt.Printf("Read written data\n")
writeBuffer.Write(*data)
writeBuffer.Flush()
case data := <-t.sendingQueue:
fmt.Printf("Read pushed data\n")
writeBuffer.Write(*data)
writeBuffer.Flush()
case <-ticker:
fmt.Printf("Tick\n")
return
}
fmt.Printf("Finished for loop\n")
}
}
utils_test.go
func TestUtils_TestingTCPServer_WritesRequest(t *testing.T) {
payload := []byte("hello world\n")
// <...> In gist here is placed INIT piece, which
// is required to debug single test
fmt.Printf("Putting payload into queue\n")
// This doesn't affect channel
err = utilTestingSrv.Put(&payload)
assert.Nil(t, err)
// This doesn't work either
//go func(queue chan *[]byte, data *[]byte) {
// queue <- data
//}(utilTestingSrv.sendingQueue, &payload)
conn, err := net.Dial("tcp", ":41123")
if !assert.Nil(t, err) {
t.Error("could not connect to server: ", err)
}
defer conn.Close()
out := make([]byte, 1024)
if _, err := conn.Read(out); assert.Nil(t, err) {
// Need to remove trailing byte 0xa from bytes array to make sure bytes array are equal.
if out[len(payload)] == 0xa {
out[len(payload)] = 0x0
}
assert.Equal(t, payload, bytes.Trim(out, "\x00"))
} else {
t.Error("could not read from connection")
}
}

Answer 1

After a help from a colleague and reading the article on how init works, I found a problem.
It was in init function, which was recreating extra server, due to using := assignment. I also updated code to make sure server runs before net.Dial and conn.Read.