receiver/zookeeper: Attempt to make test stable (open-telemetry#3274)

Attempt to make test stable by waiting till the listener is setup.

**Link to tracking Issue:** open-telemetry#3034

receiver/zookeeperreceiver/scraper_test.go

@@ -61,7 +61,6 @@ func TestZookeeperMetricsScraperScrape(t *testing.T) {
  metricsV3414 = append(metricsV3414, commonMetrics...)
  metricsV3414 = append(metricsV3414, metadata.Metrics.ZookeeperFsyncThresholdExceeds.New())
 
- localAddr := testutil.GetAvailableLocalAddress(t)
  tests := []struct {
  name string
  expectedMetrics []pdata.Metric
@@ -192,10 +191,12 @@ func TestZookeeperMetricsScraperScrape(t *testing.T) {
  }
  for _, tt := range tests {
  t.Run(tt.name, func(t *testing.T) {
+ localAddr := testutil.GetAvailableLocalAddress(t)
  if !tt.mockZKConnectionErr {
- go mockZKServer(t, localAddr, tt.mockedZKOutputSourceFilename)
+ ms := mockedServer{ready: make(chan bool, 1)}
+ go ms.mockZKServer(t, localAddr, tt.mockedZKOutputSourceFilename)
+ <-ms.ready
  }
- time.Sleep(100 * time.Millisecond)
 
  cfg := &Config{
  TCPAddr: confignet.TCPAddr{
@@ -281,11 +282,17 @@ func assertDescriptorEqual(t *testing.T, expected pdata.Metric, actual pdata.Met
  require.Equal(t, expected.DataType(), actual.DataType())
 }
 
-func mockZKServer(t *testing.T, endpoint string, filename string) {
+type mockedServer struct {
+ ready chan bool
+}
+
+func (ms *mockedServer) mockZKServer(t *testing.T, endpoint string, filename string) {
  listener, err := net.Listen("tcp", endpoint)
  require.NoError(t, err)
  defer listener.Close()
 
+ ms.ready <- true
+
  conn, err := listener.Accept()
  require.NoError(t, err)