Fix flaky OTLP exporter reconnect test (open-telemetry#1814)

* Fix flaky OTLP exporter reconnect test

The tests that check the OTLP exporter will reconnect wait for the
reconnect loop to complete, in theory. However, they do not yield the
active goroutine scheduling. The reconnect loop is in its own goroutine
meaning it is unlikely for that loop to be re-entered, especially on
slow systems. This updates the tests call runtime.Gosched when waiting
for the reconnect loop and yield the scheduling to other goroutines.

* Add changes to changelog

* Use time.After instead of Timer

* Remove changelog entry

exporters/otlp/otlpgrpc/otlp_integration_test.go

@@ -18,6 +18,7 @@ import (
 	"context"
 	"fmt"
 	"net"
+	"runtime"
 	"strings"
 	"testing"
 	"time"
@@ -144,7 +145,7 @@ func TestNewExporter_invokeStartThenStopManyTimes(t *testing.T) {
 func TestNewExporter_collectorConnectionDiesThenReconnectsWhenInRestMode(t *testing.T) {
 	mc := runMockCollector(t)
 
-	reconnectionPeriod := 2 * time.Second // 2 second + jitter rest time after reconnection
+	reconnectionPeriod := 20 * time.Millisecond
 	ctx := context.Background()
 	exp := newGRPCExporter(t, ctx, mc.endpoint,
 		otlpgrpc.WithReconnectionPeriod(reconnectionPeriod))
@@ -165,8 +166,18 @@ func TestNewExporter_collectorConnectionDiesThenReconnectsWhenInRestMode(t *test
 		mc.endpoint,
 	)
 
-	// give it time for first reconnection
-	<-time.After(time.Millisecond * 20)
+	// Give the exporter sometime to reconnect
+	func() {
+		timer := time.After(reconnectionPeriod * 10)
+		for {
+			select {
+			case <-timer:
+				return
+			default:
+				runtime.Gosched()
+			}
+		}
+	}()
 
 	// second export, it will detect connection issue, change state of exporter to disconnected and
 	// send message to disconnected channel but this time reconnection gouroutine will be in (rest mode, not listening to the disconnected channel)
@@ -184,7 +195,17 @@ func TestNewExporter_collectorConnectionDiesThenReconnectsWhenInRestMode(t *test
 
 	// make sure reconnection loop hits beginning and goes back to waiting mode
 	// after hitting beginning of the loop it should reconnect
-	<-time.After(time.Second * 4)
+	func() {
+		timer := time.After(reconnectionPeriod * 10)
+		for {
+			select {
+			case <-timer:
+				return
+			default:
+				runtime.Gosched()
+			}
+		}
+	}()
 
 	n := 10
 	for i := 0; i < n; i++ {
@@ -240,7 +261,17 @@ func TestNewExporter_collectorConnectionDiesThenReconnects(t *testing.T) {
 		nmc := runMockCollectorAtEndpoint(t, mc.endpoint)
 
 		// Give the exporter sometime to reconnect
-		<-time.After(reconnectionPeriod * 4)
+		func() {
+			timer := time.After(reconnectionPeriod * 10)
+			for {
+				select {
+				case <-timer:
+					return
+				default:
+					runtime.Gosched()
+				}
+			}
+		}()
 
 		n := 10
 		for i := 0; i < n; i++ {