feat: add watcher for record code excution time

function/watcher_test.go

@@ -0,0 +1,32 @@
+package function
+
+import (
+	"testing"
+)
+
+func TestWatcher(t *testing.T) {
+	w := &Watcher{}
+	w.Start()
+
+	longRunningTask()
+
+	if !w.excuting {
+		t.FailNow()
+	}
+
+	w.Stop()
+
+	eapsedTime := w.GetElapsedTime().Milliseconds()
+	t.Log("Elapsed Time (milsecond)", eapsedTime)
+
+	if w.excuting {
+		t.FailNow()
+	}
+}
+
+func longRunningTask() {
+	var slice []int64
+	for i := 0; i < 10000000; i++ {
+		slice = append(slice, int64(i))
+	}
+}