tcp/udp listeners, remove locks & improve test coverage

testutil/accumulator.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"reflect"
 	"sync"
+	"sync/atomic"
 	"testing"
 	"time"
 
@@ -27,9 +28,11 @@ func (p *Metric) String() string {
 type Accumulator struct {
 	sync.Mutex
 
-	Metrics []*Metric
-	Errors  []error
-	debug   bool
+	Metrics  []*Metric
+	nMetrics uint64
+	Discard  bool
+	Errors   []error
+	debug    bool
 }
 
 // Add adds a measurement point to the accumulator
@@ -43,6 +46,10 @@ func (a *Accumulator) Add(
 	a.AddFields(measurement, fields, tags, t...)
 }
 
+func (a *Accumulator) NMetrics() uint64 {
+	return atomic.LoadUint64(&a.nMetrics)
+}
+
 // AddFields adds a measurement point with a specified timestamp.
 func (a *Accumulator) AddFields(
 	measurement string,
@@ -50,6 +57,10 @@ func (a *Accumulator) AddFields(
 	tags map[string]string,
 	timestamp ...time.Time,
 ) {
+	atomic.AddUint64(&a.nMetrics, 1)
+	if a.Discard {
+		return
+	}
 	a.Lock()
 	defer a.Unlock()
 	if tags == nil {