Add Timespan Func with Initial Value (#27)

* update func

* unit test fix

* fix edge case

* lint fix

* unit test logic

* update to value

stats.go

@@ -149,14 +149,20 @@ type Timer interface {
 // They measure time from the time they are allocated by a Timer with
 //   AllocateSpan()
 // until they call
-//   Complete().
+//   Complete()
+// or
+//   CompleteWithDuration(time.Duration)
+// When either function is called the timespan is flushed.
 // When Complete is called the timespan is flushed.
 //
 // A Timespan can be flushed at function
 // return by calling Complete with golang's defer statement.
 type Timespan interface {
 	// End the Timespan and flush it.
 	Complete()
+
+	// End the Timespan and flush it. Adds additional time.Duration to the measured time
+	CompleteWithDuration(time.Duration)
 }
 
 // A StatGenerator can be used to programatically generate stats.
@@ -288,6 +294,10 @@ func (ts *timespan) Complete() {
 	ts.timer.time(time.Now().Sub(ts.start))
 }
 
+func (ts *timespan) CompleteWithDuration(value time.Duration) {
+	ts.timer.time(value)
+}
+
 type statStore struct {
 	countersMtx sync.RWMutex
 	counters    map[string]*counter

stats_test.go

@@ -3,6 +3,7 @@ package stats
 import (
 	"math/rand"
 	"strconv"
+	"strings"
 	"sync"
 	"testing"
 	"time"
@@ -35,6 +36,21 @@ func TestStats(t *testing.T) {
 	wg.Wait()
 }
 
+// Ensure timers and timespans are working
+func TestTimer(t *testing.T) {
+	testDuration := time.Duration(9800000)
+	sink := &testStatSink{}
+	store := NewStore(sink, true)
+	store.NewTimer("test").AllocateSpan().CompleteWithDuration(testDuration)
+	store.Flush()
+
+	expected := "test:9800.000000|ms"
+	timer := sink.record
+	if !strings.Contains(timer, expected) {
+		t.Error("wanted timer value of test:9800.000000|ms, got", timer)
+	}
+}
+
 var bmID = ""
 var bmVal = uint64(0)