diff --git a/README.md b/README.md
index 85d91fa..4a00b99 100644
--- a/README.md
+++ b/README.md
@@ -6,9 +6,10 @@
 
 
 [![Build Status][1]][2]
-[![godoc for panjf2000/ants][3]][4]
+[![codecov][3]][4]
 [![goreportcard for panjf2000/ants][5]][6]
-[![MIT Licence][7]][8]
+[![godoc for panjf2000/ants][7]][8]
+[![MIT Licence][9]][10]
 
 [中文项目说明](README_ZH.md) | [Project Tutorial](http://blog.taohuawu.club/article/42)
 
@@ -185,9 +186,11 @@ There was only the test of `ants` Pool because my computer was crash when it rea
 
 [1]: https://travis-ci.com/panjf2000/ants.svg?branch=develop
 [2]: https://travis-ci.com/panjf2000/ants
-[3]: https://godoc.org/github.com/panjf2000/ants?status.svg
-[4]: https://godoc.org/github.com/panjf2000/ants
+[3]: https://codecov.io/gh/panjf2000/ants
+[4]: https://codecov.io/gh/panjf2000/ants/branch/develop/graph/badge.svg
 [5]: https://goreportcard.com/badge/github.com/panjf2000/ants
 [6]: https://goreportcard.com/report/github.com/panjf2000/ants
-[7]: https://badges.frapsoft.com/os/mit/mit.svg?v=103
-[8]: https://opensource.org/licenses/mit-license.php
+[7]: https://godoc.org/github.com/panjf2000/ants?status.svg
+[8]: https://godoc.org/github.com/panjf2000/ants
+[9]: https://badges.frapsoft.com/os/mit/mit.svg?v=103
+[10]: https://opensource.org/licenses/mit-license.php
diff --git a/ants_benchmark_test.go b/ants_benchmark_test.go
index c8623aa..440a3c8 100644
--- a/ants_benchmark_test.go
+++ b/ants_benchmark_test.go
@@ -44,7 +44,7 @@ const (
 const (
 	RunTimes = 10000000
 	Param    = 10
-	AntsSize = 100000
+	AntsSize = 50000
 )
 
 func demoFunc() error {
diff --git a/ants_test.go b/ants_test.go
index 18b5ffb..72250b4 100644
--- a/ants_test.go
+++ b/ants_test.go
@@ -65,6 +65,10 @@ func TestAntsPool(t *testing.T) {
 	}
 	wg.Wait()
 
+	t.Logf("pool, capacity:%d", ants.Cap())
+	t.Logf("pool, running workers number:%d", ants.Running())
+	t.Logf("pool, free workers number:%d", ants.Free())
+
 	mem := runtime.MemStats{}
 	runtime.ReadMemStats(&mem)
 	t.Logf("memory usage:%d MB", mem.TotalAlloc/MiB)
@@ -87,7 +91,17 @@ func TestNoPool(t *testing.T) {
 }
 
 func TestCodeCov(t *testing.T) {
+	_, err := ants.NewTimingPool(-1, -1)
+	t.Log(err)
+	_, err = ants.NewTimingPool(1, -1)
+	t.Log(err)
+	_, err = ants.NewTimingPoolWithFunc(-1, -1, demoPoolFunc)
+	t.Log(err)
+	_, err = ants.NewTimingPoolWithFunc(1, -1, demoPoolFunc)
+	t.Log(err)
+
 	p0, _ := ants.NewPool(AntsSize)
+	defer p0.Submit(demoFunc)
 	defer p0.Release()
 	for i := 0; i < n; i++ {
 		p0.Submit(demoFunc)
@@ -95,10 +109,12 @@ func TestCodeCov(t *testing.T) {
 	t.Logf("pool, capacity:%d", p0.Cap())
 	t.Logf("pool, running workers number:%d", p0.Running())
 	t.Logf("pool, free workers number:%d", p0.Free())
+	p0.ReSize(AntsSize)
 	p0.ReSize(AntsSize / 2)
 	t.Logf("pool, after resize, capacity:%d", p0.Cap())
 
 	p, _ := ants.NewPoolWithFunc(AntsSize, demoPoolFunc)
+	defer p.Serve(Param)
 	defer p.Release()
 	for i := 0; i < n; i++ {
 		p.Serve(Param)
@@ -106,6 +122,7 @@ func TestCodeCov(t *testing.T) {
 	t.Logf("pool with func, capacity:%d", p.Cap())
 	t.Logf("pool with func, running workers number:%d", p.Running())
 	t.Logf("pool with func, free workers number:%d", p.Free())
+	p.ReSize(AntsSize)
 	p.ReSize(AntsSize / 2)
 	t.Logf("pool with func, after resize, capacity:%d", p.Cap())
 }
diff --git a/pool.go b/pool.go
index c832c9b..3f988aa 100644
--- a/pool.go
+++ b/pool.go
@@ -146,9 +146,6 @@ func (p *Pool) Release() error {
 			p.getWorker().task <- nil
 		}
 		p.lock.Lock()
-		for i := range p.workers {
-			p.workers[i] = nil
-		}
 		p.workers = nil
 		p.lock.Unlock()
 	})
diff --git a/pool_func.go b/pool_func.go
index 7040f83..c4dea88 100644
--- a/pool_func.go
+++ b/pool_func.go
@@ -151,9 +151,6 @@ func (p *PoolWithFunc) Release() error {
 			p.getWorker().args <- nil
 		}
 		p.lock.Lock()
-		for i := range p.workers {
-			p.workers[i] = nil
-		}
 		p.workers = nil
 		p.lock.Unlock()
 	})