Add docker input server version (#4035)

testutil/accumulator.go

@@ -65,8 +65,15 @@ func (a *Accumulator) AddFields(
 	if a.Discard {
 		return
 	}
-	if tags == nil {
-		tags = map[string]string{}
+
+	tagsCopy := map[string]string{}
+	for k, v := range tags {
+		tagsCopy[k] = v
+	}
+
+	fieldsCopy := map[string]interface{}{}
+	for k, v := range fields {
+		fieldsCopy[k] = v
 	}
 
 	if len(fields) == 0 {
@@ -91,7 +98,7 @@ func (a *Accumulator) AddFields(
 	p := &Metric{
 		Measurement: measurement,
 		Fields:      fields,
-		Tags:        tags,
+		Tags:        tagsCopy,
 		Time:        t,
 	}