Add SerializeBatch method to the Serializer interface (#4107)

plugins/serializers/influx/influx_test.go

@@ -447,3 +447,24 @@ func BenchmarkSerializer(b *testing.B) {
 		})
 	}
 }
+
+func TestSerialize_SerializeBatch(t *testing.T) {
+	m := MustMetric(
+		metric.New(
+			"cpu",
+			map[string]string{},
+			map[string]interface{}{
+				"value": 42.0,
+			},
+			time.Unix(0, 0),
+		),
+	)
+
+	metrics := []telegraf.Metric{m, m}
+
+	serializer := NewSerializer()
+	serializer.SetFieldSortOrder(SortFields)
+	output, err := serializer.SerializeBatch(metrics)
+	require.NoError(t, err)
+	require.Equal(t, []byte("cpu value=42 0\ncpu value=42 0\n"), output)
+}