otelgrpc: Stablize TestInterceptors (#4535)

Author: pellared

instrumentation/google.golang.org/grpc/otelgrpc/test/grpc_test.go

@@ -19,6 +19,7 @@ import (
 	"net"
 	"strconv"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
@@ -136,6 +137,12 @@ func TestInterceptors(t *testing.T) {
 	})
 
 	t.Run("StreamClientSpans", func(t *testing.T) {
+		// StreamClientInterceptor ends the spans asynchronously.
+		// We need to wait for all spans before asserting them.
+		require.EventuallyWithT(t, func(c *assert.CollectT) {
+			assert.Len(c, clientStreamSR.Ended(), 3)
+		}, 5*time.Second, 100*time.Millisecond)
+
 		checkStreamClientSpans(t, clientStreamSR.Ended(), listener.Addr().String())
 	})