diff --git a/debug/gdebug/gdebug_stack.go b/debug/gdebug/gdebug_stack.go
index 522960803..67ec3e30e 100644
--- a/debug/gdebug/gdebug_stack.go
+++ b/debug/gdebug/gdebug_stack.go
@@ -9,7 +9,6 @@ package gdebug
 import (
 	"bytes"
 	"fmt"
-	"path/filepath"
 	"runtime"
 	"strings"
 )
@@ -72,10 +71,6 @@ func StackWithFilters(filters []string, skip ...int) string {
 			// Custom filtering.
 			filtered = false
 			for _, filter := range filters {
-				// Ignore test files.
-				if strings.HasSuffix(filepath.Base(file), "_test.go") {
-					break
-				}
 				if filter != "" && strings.Contains(file, filter) {
 					filtered = true
 					break
diff --git a/os/gcache/gcache.go b/os/gcache/gcache.go
index fd4dc0f5a..80ef28aab 100644
--- a/os/gcache/gcache.go
+++ b/os/gcache/gcache.go
@@ -13,9 +13,6 @@ import (
 	"time"
 )
 
-// ValueFunc is the function for custom cache value producing.
-type ValueFunc func() (value interface{}, err error)
-
 // Default cache object.
 var defaultCache = New()
 
@@ -61,7 +58,7 @@ func GetOrSet(key interface{}, value interface{}, duration time.Duration) (inter
 // GetOrSetFunc returns the value of <key>, or sets <key> with result of function <f>
 // and returns its result if <key> does not exist in the cache. The key-value pair expires
 // after <duration>. It does not expire if <duration> == 0.
-func GetOrSetFunc(key interface{}, f ValueFunc, duration time.Duration) (interface{}, error) {
+func GetOrSetFunc(key interface{}, f func() (interface{}, error), duration time.Duration) (interface{}, error) {
 	return defaultCache.GetOrSetFunc(key, f, duration)
 }
 
@@ -70,7 +67,7 @@ func GetOrSetFunc(key interface{}, f ValueFunc, duration time.Duration) (interfa
 // after <duration>. It does not expire if <duration> == 0.
 //
 // Note that the function <f> is executed within writing mutex lock.
-func GetOrSetFuncLock(key interface{}, f ValueFunc, duration time.Duration) (interface{}, error) {
+func GetOrSetFuncLock(key interface{}, f func() (interface{}, error), duration time.Duration) (interface{}, error) {
 	return defaultCache.GetOrSetFuncLock(key, f, duration)
 }
 
diff --git a/os/gcache/gcache_adapter.go b/os/gcache/gcache_adapter.go
index 28a022895..1dad55efe 100644
--- a/os/gcache/gcache_adapter.go
+++ b/os/gcache/gcache_adapter.go
@@ -55,7 +55,7 @@ type Adapter interface {
 	// It does not expire if <duration> == 0.
 	// It deletes the <key> if <duration> < 0 or given <value> is nil, but it does nothing
 	// if <value> is a function and the function result is nil.
-	GetOrSetFunc(key interface{}, f ValueFunc, duration time.Duration) (interface{}, error)
+	GetOrSetFunc(key interface{}, f func() (interface{}, error), duration time.Duration) (interface{}, error)
 
 	// GetOrSetFuncLock retrieves and returns the value of <key>, or sets <key> with result of
 	// function <f> and returns its result if <key> does not exist in the cache. The key-value
@@ -66,7 +66,7 @@ type Adapter interface {
 	//
 	// Note that the function <f> should be executed within writing mutex lock for concurrent
 	// safety purpose.
-	GetOrSetFuncLock(key interface{}, f ValueFunc, duration time.Duration) (interface{}, error)
+	GetOrSetFuncLock(key interface{}, f func() (interface{}, error), duration time.Duration) (interface{}, error)
 
 	// Contains returns true if <key> exists in the cache, or else returns false.
 	Contains(key interface{}) (bool, error)
diff --git a/os/gcache/gcache_adapter_memory.go b/os/gcache/gcache_adapter_memory.go
index 2eb7e9a5d..5dd532c61 100644
--- a/os/gcache/gcache_adapter_memory.go
+++ b/os/gcache/gcache_adapter_memory.go
@@ -252,7 +252,7 @@ func (c *adapterMemory) GetOrSet(key interface{}, value interface{}, duration ti
 // It does not expire if <duration> == 0.
 // It deletes the <key> if <duration> < 0 or given <value> is nil, but it does nothing
 // if <value> is a function and the function result is nil.
-func (c *adapterMemory) GetOrSetFunc(key interface{}, f ValueFunc, duration time.Duration) (interface{}, error) {
+func (c *adapterMemory) GetOrSetFunc(key interface{}, f func() (interface{}, error), duration time.Duration) (interface{}, error) {
 	v, err := c.Get(key)
 	if err != nil {
 		return nil, err
@@ -280,7 +280,7 @@ func (c *adapterMemory) GetOrSetFunc(key interface{}, f ValueFunc, duration time
 //
 // Note that the function <f> should be executed within writing mutex lock for concurrent
 // safety purpose.
-func (c *adapterMemory) GetOrSetFuncLock(key interface{}, f ValueFunc, duration time.Duration) (interface{}, error) {
+func (c *adapterMemory) GetOrSetFuncLock(key interface{}, f func() (interface{}, error), duration time.Duration) (interface{}, error) {
 	v, err := c.Get(key)
 	if err != nil {
 		return nil, err
@@ -401,7 +401,7 @@ func (c *adapterMemory) doSetWithLockCheck(key interface{}, value interface{}, d
 	if v, ok := c.data[key]; ok && !v.IsExpired() {
 		return v.v, nil
 	}
-	if f, ok := value.(ValueFunc); ok {
+	if f, ok := value.(func() (interface{}, error)); ok {
 		v, err := f()
 		if err != nil {
 			return nil, err
diff --git a/os/gfsnotify/gfsnotify_watcher_loop.go b/os/gfsnotify/gfsnotify_watcher_loop.go
index 733b55220..c9ada4006 100644
--- a/os/gfsnotify/gfsnotify_watcher_loop.go
+++ b/os/gfsnotify/gfsnotify_watcher_loop.go
@@ -23,14 +23,14 @@ func (w *Watcher) startWatchLoop() {
 			// Event listening.
 			case ev := <-w.watcher.Events:
 				// Filter the repeated event in custom duration.
-				w.cache.SetIfNotExist(ev.String(), func() interface{} {
+				w.cache.SetIfNotExist(ev.String(), func() (interface{}, error) {
 					w.events.Push(&Event{
 						event:   ev,
 						Path:    ev.Name,
 						Op:      Op(ev.Op),
 						Watcher: w,
 					})
-					return struct{}{}
+					return struct{}{}, nil
 				}, repeatEventFilterDuration)
 
 			case err := <-w.watcher.Errors: