Add override processor (#3773)

This plugin can perform the standard metric modifications using override semantics.

plugins/processors/override/override_test.go

@@ -0,0 +1,80 @@
+package override
+
+import (
+	"testing"
+	"time"
+
+	"github.com/influxdata/telegraf"
+	"github.com/influxdata/telegraf/metric"
+	"github.com/stretchr/testify/assert"
+)
+
+func createTestMetric() telegraf.Metric {
+	metric, _ := metric.New("m1",
+		map[string]string{"metric_tag": "from_metric"},
+		map[string]interface{}{"value": int64(1)},
+		time.Now(),
+	)
+	return metric
+}
+
+func calculateProcessedTags(processor Override, metric telegraf.Metric) map[string]string {
+	processed := processor.Apply(metric)
+	return processed[0].Tags()
+}
+
+func TestRetainsTags(t *testing.T) {
+	processor := Override{}
+
+	tags := calculateProcessedTags(processor, createTestMetric())
+
+	value, present := tags["metric_tag"]
+	assert.True(t, present, "Tag of metric was not present")
+	assert.Equal(t, "from_metric", value, "Value of Tag was changed")
+}
+
+func TestAddTags(t *testing.T) {
+	processor := Override{Tags: map[string]string{"added_tag": "from_config", "another_tag": ""}}
+
+	tags := calculateProcessedTags(processor, createTestMetric())
+
+	value, present := tags["added_tag"]
+	assert.True(t, present, "Additional Tag of metric was not present")
+	assert.Equal(t, "from_config", value, "Value of Tag was changed")
+	assert.Equal(t, 3, len(tags), "Should have one previous and two added tags.")
+}
+
+func TestOverwritesPresentTagValues(t *testing.T) {
+	processor := Override{Tags: map[string]string{"metric_tag": "from_config"}}
+
+	tags := calculateProcessedTags(processor, createTestMetric())
+
+	value, present := tags["metric_tag"]
+	assert.True(t, present, "Tag of metric was not present")
+	assert.Equal(t, 1, len(tags), "Should only have one tag.")
+	assert.Equal(t, "from_config", value, "Value of Tag was not changed")
+}
+
+func TestOverridesName(t *testing.T) {
+	processor := Override{NameOverride: "overridden"}
+
+	processed := processor.Apply(createTestMetric())
+
+	assert.Equal(t, "overridden", processed[0].Name(), "Name was not overridden")
+}
+
+func TestNamePrefix(t *testing.T) {
+	processor := Override{NamePrefix: "Pre-"}
+
+	processed := processor.Apply(createTestMetric())
+
+	assert.Equal(t, "Pre-m1", processed[0].Name(), "Prefix was not applied")
+}
+
+func TestNameSuffix(t *testing.T) {
+	processor := Override{NameSuffix: "-suff"}
+
+	processed := processor.Apply(createTestMetric())
+
+	assert.Equal(t, "m1-suff", processed[0].Name(), "Suffix was not applied")
+}