Use lifo order in metric buffer (#5287)

internal/models/running_output_test.go

@@ -7,7 +7,6 @@ import (
 
 	"github.com/influxdata/telegraf"
 	"github.com/influxdata/telegraf/testutil"
-
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -28,6 +27,14 @@ var next5 = []telegraf.Metric{
 	testutil.TestMetric(101, "metric10"),
 }
 
+func reverse(metrics []telegraf.Metric) []telegraf.Metric {
+	result := make([]telegraf.Metric, 0, len(metrics))
+	for i := len(metrics) - 1; i >= 0; i-- {
+		result = append(result, metrics[i])
+	}
+	return result
+}
+
 // Benchmark adding metrics.
 func BenchmarkRunningOutputAddWrite(b *testing.B) {
 	conf := &OutputConfig{
@@ -297,7 +304,7 @@ func TestRunningOutputWriteFailOrder(t *testing.T) {
 	// Verify that 10 metrics were written
 	assert.Len(t, m.Metrics(), 10)
 	// Verify that they are in order
-	expected := append(first5, next5...)
+	expected := append(reverse(next5), reverse(first5)...)
 	assert.Equal(t, expected, m.Metrics())
 }
 
@@ -355,24 +362,17 @@ func TestRunningOutputWriteFailOrder2(t *testing.T) {
 	err = ro.Write()
 	require.NoError(t, err)
 
-	// Verify that 10 metrics were written
+	// Verify that 20 metrics were written
 	assert.Len(t, m.Metrics(), 20)
 	// Verify that they are in order
-	expected := append(first5, next5...)
-	expected = append(expected, first5...)
-	expected = append(expected, next5...)
+	expected := append(reverse(next5), reverse(first5)...)
+	expected = append(expected, reverse(next5)...)
+	expected = append(expected, reverse(first5)...)
 	assert.Equal(t, expected, m.Metrics())
 }
 
 // Verify that the order of points is preserved when there is a remainder
 // of points for the batch.
-//
-// ie, with a batch size of 5:
-//
-//     1 2 3 4 5 6 <-- order, failed points
-//     6 1 2 3 4 5 <-- order, after 1st write failure (1 2 3 4 5 was batch)
-//     1 2 3 4 5 6 <-- order, after 2nd write failure, (6 was batch)
-//
 func TestRunningOutputWriteFailOrder3(t *testing.T) {
 	conf := &OutputConfig{
 		Filter: Filter{},
@@ -408,7 +408,7 @@ func TestRunningOutputWriteFailOrder3(t *testing.T) {
 	// Verify that 6 metrics were written
 	assert.Len(t, m.Metrics(), 6)
 	// Verify that they are in order
-	expected := append(first5, next5[0])
+	expected := []telegraf.Metric{next5[0], first5[4], first5[3], first5[2], first5[1], first5[0]}
 	assert.Equal(t, expected, m.Metrics())
 }