diff --git a/consumer.go b/consumer.go
index 96af040..da3e79d 100644
--- a/consumer.go
+++ b/consumer.go
@@ -7,16 +7,18 @@ import (
 	"sync"
 	"sync/atomic"
 	"time"
+
+	"github.com/golang-queue/queue/core"
 )
 
-var _ Worker = (*Consumer)(nil)
+var _ core.Worker = (*Consumer)(nil)
 
 var errMaxCapacity = errors.New("max capacity reached")
 
 // Consumer for simple queue using buffer channel
 type Consumer struct {
-	taskQueue chan QueuedMessage
-	runFunc   func(context.Context, QueuedMessage) error
+	taskQueue chan core.QueuedMessage
+	runFunc   func(context.Context, core.QueuedMessage) error
 	stop      chan struct{}
 	logger    Logger
 	stopOnce  sync.Once
@@ -75,7 +77,7 @@ func (s *Consumer) handle(job Job) error {
 }
 
 // Run to execute new task
-func (s *Consumer) Run(task QueuedMessage) error {
+func (s *Consumer) Run(task core.QueuedMessage) error {
 	var data Job
 	_ = json.Unmarshal(task.Bytes(), &data)
 	if v, ok := task.(Job); ok {
@@ -104,7 +106,7 @@ func (s *Consumer) Shutdown() error {
 }
 
 // Queue send task to the buffer channel
-func (s *Consumer) Queue(task QueuedMessage) error {
+func (s *Consumer) Queue(task core.QueuedMessage) error {
 	if atomic.LoadInt32(&s.stopFlag) == 1 {
 		return ErrQueueShutdown
 	}
@@ -118,7 +120,7 @@ func (s *Consumer) Queue(task QueuedMessage) error {
 }
 
 // Request a new task from channel
-func (s *Consumer) Request() (QueuedMessage, error) {
+func (s *Consumer) Request() (core.QueuedMessage, error) {
 	clock := 0
 loop:
 	for {
@@ -143,7 +145,7 @@ loop:
 func NewConsumer(opts ...Option) *Consumer {
 	o := NewOptions(opts...)
 	w := &Consumer{
-		taskQueue: make(chan QueuedMessage, o.queueSize),
+		taskQueue: make(chan core.QueuedMessage, o.queueSize),
 		stop:      make(chan struct{}),
 		logger:    o.logger,
 		runFunc:   o.fn,
diff --git a/consumer_test.go b/consumer_test.go
index 02a0f16..ba013b4 100644
--- a/consumer_test.go
+++ b/consumer_test.go
@@ -9,6 +9,8 @@ import (
 	"testing"
 	"time"
 
+	"github.com/golang-queue/queue/core"
+
 	"github.com/stretchr/testify/assert"
 )
 
@@ -28,7 +30,7 @@ func TestCustomFuncAndWait(t *testing.T) {
 		message: "foo",
 	}
 	w := NewConsumer(
-		WithFn(func(ctx context.Context, m QueuedMessage) error {
+		WithFn(func(ctx context.Context, m core.QueuedMessage) error {
 			time.Sleep(500 * time.Millisecond)
 			return nil
 		}),
@@ -77,7 +79,7 @@ func TestJobReachTimeout(t *testing.T) {
 		message: "foo",
 	}
 	w := NewConsumer(
-		WithFn(func(ctx context.Context, m QueuedMessage) error {
+		WithFn(func(ctx context.Context, m core.QueuedMessage) error {
 			for {
 				select {
 				case <-ctx.Done():
@@ -111,7 +113,7 @@ func TestCancelJobAfterShutdown(t *testing.T) {
 	}
 	w := NewConsumer(
 		WithLogger(NewEmptyLogger()),
-		WithFn(func(ctx context.Context, m QueuedMessage) error {
+		WithFn(func(ctx context.Context, m core.QueuedMessage) error {
 			for {
 				select {
 				case <-ctx.Done():
@@ -144,7 +146,7 @@ func TestCancelJobAfterShutdown(t *testing.T) {
 func TestGoroutineLeak(t *testing.T) {
 	w := NewConsumer(
 		WithLogger(NewLogger()),
-		WithFn(func(ctx context.Context, m QueuedMessage) error {
+		WithFn(func(ctx context.Context, m core.QueuedMessage) error {
 			for {
 				select {
 				case <-ctx.Done():
@@ -187,7 +189,7 @@ func TestGoroutinePanic(t *testing.T) {
 		message: "foo",
 	}
 	w := NewConsumer(
-		WithFn(func(ctx context.Context, m QueuedMessage) error {
+		WithFn(func(ctx context.Context, m core.QueuedMessage) error {
 			panic("missing something")
 		}),
 	)
@@ -208,7 +210,7 @@ func TestHandleTimeout(t *testing.T) {
 		Payload: []byte("foo"),
 	}
 	w := NewConsumer(
-		WithFn(func(ctx context.Context, m QueuedMessage) error {
+		WithFn(func(ctx context.Context, m core.QueuedMessage) error {
 			time.Sleep(200 * time.Millisecond)
 			return nil
 		}),
@@ -224,7 +226,7 @@ func TestHandleTimeout(t *testing.T) {
 	}
 
 	w = NewConsumer(
-		WithFn(func(ctx context.Context, m QueuedMessage) error {
+		WithFn(func(ctx context.Context, m core.QueuedMessage) error {
 			time.Sleep(200 * time.Millisecond)
 			return nil
 		}),
@@ -248,7 +250,7 @@ func TestJobComplete(t *testing.T) {
 		Payload: []byte("foo"),
 	}
 	w := NewConsumer(
-		WithFn(func(ctx context.Context, m QueuedMessage) error {
+		WithFn(func(ctx context.Context, m core.QueuedMessage) error {
 			return errors.New("job completed")
 		}),
 	)
@@ -263,7 +265,7 @@ func TestJobComplete(t *testing.T) {
 	}
 
 	w = NewConsumer(
-		WithFn(func(ctx context.Context, m QueuedMessage) error {
+		WithFn(func(ctx context.Context, m core.QueuedMessage) error {
 			time.Sleep(200 * time.Millisecond)
 			return errors.New("job completed")
 		}),
@@ -324,7 +326,7 @@ func TestTaskJobComplete(t *testing.T) {
 func TestIncreaseWorkerCount(t *testing.T) {
 	w := NewConsumer(
 		WithLogger(NewEmptyLogger()),
-		WithFn(func(ctx context.Context, m QueuedMessage) error {
+		WithFn(func(ctx context.Context, m core.QueuedMessage) error {
 			time.Sleep(500 * time.Millisecond)
 			return nil
 		}),
@@ -354,7 +356,7 @@ func TestIncreaseWorkerCount(t *testing.T) {
 
 func TestDecreaseWorkerCount(t *testing.T) {
 	w := NewConsumer(
-		WithFn(func(ctx context.Context, m QueuedMessage) error {
+		WithFn(func(ctx context.Context, m core.QueuedMessage) error {
 			time.Sleep(100 * time.Millisecond)
 			return nil
 		}),
diff --git a/worker.go b/core/worker.go
similarity index 96%
rename from worker.go
rename to core/worker.go
index e246613..61f5bc2 100644
--- a/worker.go
+++ b/core/worker.go
@@ -1,4 +1,4 @@
-package queue
+package core
 
 // Worker interface
 type Worker interface {
diff --git a/go.mod b/go.mod
index 7507553..94dfa70 100644
--- a/go.mod
+++ b/go.mod
@@ -3,6 +3,7 @@ module github.com/golang-queue/queue
 go 1.18
 
 require (
+	github.com/golang/mock v1.6.0
 	github.com/stretchr/testify v1.7.1
 	go.uber.org/goleak v1.1.12
 )
diff --git a/go.sum b/go.sum
index addf9a6..9320fa5 100644
--- a/go.sum
+++ b/go.sum
@@ -1,5 +1,7 @@
 github.com/davecgh/go-spew v1.1.0 h1:ZDRjVQ15GmhC3fiQ8ni8+OwkZQO4DARzQgrnXU1Liz8=
 github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/golang/mock v1.6.0 h1:ErTB+efbowRARo13NNdxyJji2egdxLGQhRaY+DUumQc=
+github.com/golang/mock v1.6.0/go.mod h1:p6yTPP+5HYm5mzsMV8JkE6ZKdX+/wYM6Hr+LicevLPs=
 github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
@@ -36,6 +38,7 @@ golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20190311212946-11955173bddd/go.mod h1:LCzVGOaR6xXOjkQ3onu1FJEFr0SW1gC7cKk1uF8kGRs=
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
+golang.org/x/tools v0.1.1/go.mod h1:o0xws9oXOQQZyjljx8fwUC0k7L1pTE6eaCbjGeHmOkk=
 golang.org/x/tools v0.1.5 h1:ouewzE6p+/VEB31YYnTbEJdi8pFqKp4P4n85vwo3DHA=
 golang.org/x/tools v0.1.5/go.mod h1:o0xws9oXOQQZyjljx8fwUC0k7L1pTE6eaCbjGeHmOkk=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
diff --git a/metric_test.go b/metric_test.go
index 5bea48c..8f6e9a6 100644
--- a/metric_test.go
+++ b/metric_test.go
@@ -6,12 +6,14 @@ import (
 	"testing"
 	"time"
 
+	"github.com/golang-queue/queue/core"
+
 	"github.com/stretchr/testify/assert"
 )
 
 func TestMetricData(t *testing.T) {
 	w := NewConsumer(
-		WithFn(func(ctx context.Context, m QueuedMessage) error {
+		WithFn(func(ctx context.Context, m core.QueuedMessage) error {
 			switch string(m.Bytes()) {
 			case "foo1":
 				panic("missing something")
diff --git a/mocks/mock_message.go b/mocks/mock_message.go
new file mode 100644
index 0000000..13d4e2c
--- /dev/null
+++ b/mocks/mock_message.go
@@ -0,0 +1,48 @@
+// Code generated by MockGen. DO NOT EDIT.
+// Source: github.com/golang-queue/queue/core (interfaces: QueuedMessage)
+
+// Package mocks is a generated GoMock package.
+package mocks
+
+import (
+	reflect "reflect"
+
+	gomock "github.com/golang/mock/gomock"
+)
+
+// MockQueuedMessage is a mock of QueuedMessage interface.
+type MockQueuedMessage struct {
+	ctrl     *gomock.Controller
+	recorder *MockQueuedMessageMockRecorder
+}
+
+// MockQueuedMessageMockRecorder is the mock recorder for MockQueuedMessage.
+type MockQueuedMessageMockRecorder struct {
+	mock *MockQueuedMessage
+}
+
+// NewMockQueuedMessage creates a new mock instance.
+func NewMockQueuedMessage(ctrl *gomock.Controller) *MockQueuedMessage {
+	mock := &MockQueuedMessage{ctrl: ctrl}
+	mock.recorder = &MockQueuedMessageMockRecorder{mock}
+	return mock
+}
+
+// EXPECT returns an object that allows the caller to indicate expected use.
+func (m *MockQueuedMessage) EXPECT() *MockQueuedMessageMockRecorder {
+	return m.recorder
+}
+
+// Bytes mocks base method.
+func (m *MockQueuedMessage) Bytes() []byte {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "Bytes")
+	ret0, _ := ret[0].([]byte)
+	return ret0
+}
+
+// Bytes indicates an expected call of Bytes.
+func (mr *MockQueuedMessageMockRecorder) Bytes() *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Bytes", reflect.TypeOf((*MockQueuedMessage)(nil).Bytes))
+}
diff --git a/mocks/mock_worker.go b/mocks/mock_worker.go
new file mode 100644
index 0000000..1d50bca
--- /dev/null
+++ b/mocks/mock_worker.go
@@ -0,0 +1,92 @@
+// Code generated by MockGen. DO NOT EDIT.
+// Source: github.com/golang-queue/queue/core (interfaces: Worker)
+
+// Package mocks is a generated GoMock package.
+package mocks
+
+import (
+	reflect "reflect"
+
+	core "github.com/golang-queue/queue/core"
+	gomock "github.com/golang/mock/gomock"
+)
+
+// MockWorker is a mock of Worker interface.
+type MockWorker struct {
+	ctrl     *gomock.Controller
+	recorder *MockWorkerMockRecorder
+}
+
+// MockWorkerMockRecorder is the mock recorder for MockWorker.
+type MockWorkerMockRecorder struct {
+	mock *MockWorker
+}
+
+// NewMockWorker creates a new mock instance.
+func NewMockWorker(ctrl *gomock.Controller) *MockWorker {
+	mock := &MockWorker{ctrl: ctrl}
+	mock.recorder = &MockWorkerMockRecorder{mock}
+	return mock
+}
+
+// EXPECT returns an object that allows the caller to indicate expected use.
+func (m *MockWorker) EXPECT() *MockWorkerMockRecorder {
+	return m.recorder
+}
+
+// Queue mocks base method.
+func (m *MockWorker) Queue(arg0 core.QueuedMessage) error {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "Queue", arg0)
+	ret0, _ := ret[0].(error)
+	return ret0
+}
+
+// Queue indicates an expected call of Queue.
+func (mr *MockWorkerMockRecorder) Queue(arg0 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Queue", reflect.TypeOf((*MockWorker)(nil).Queue), arg0)
+}
+
+// Request mocks base method.
+func (m *MockWorker) Request() (core.QueuedMessage, error) {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "Request")
+	ret0, _ := ret[0].(core.QueuedMessage)
+	ret1, _ := ret[1].(error)
+	return ret0, ret1
+}
+
+// Request indicates an expected call of Request.
+func (mr *MockWorkerMockRecorder) Request() *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Request", reflect.TypeOf((*MockWorker)(nil).Request))
+}
+
+// Run mocks base method.
+func (m *MockWorker) Run(arg0 core.QueuedMessage) error {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "Run", arg0)
+	ret0, _ := ret[0].(error)
+	return ret0
+}
+
+// Run indicates an expected call of Run.
+func (mr *MockWorkerMockRecorder) Run(arg0 interface{}) *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Run", reflect.TypeOf((*MockWorker)(nil).Run), arg0)
+}
+
+// Shutdown mocks base method.
+func (m *MockWorker) Shutdown() error {
+	m.ctrl.T.Helper()
+	ret := m.ctrl.Call(m, "Shutdown")
+	ret0, _ := ret[0].(error)
+	return ret0
+}
+
+// Shutdown indicates an expected call of Shutdown.
+func (mr *MockWorkerMockRecorder) Shutdown() *gomock.Call {
+	mr.mock.ctrl.T.Helper()
+	return mr.mock.ctrl.RecordCallWithMethodType(mr.mock, "Shutdown", reflect.TypeOf((*MockWorker)(nil).Shutdown))
+}
diff --git a/mocks/mocks.go b/mocks/mocks.go
new file mode 100644
index 0000000..f87860c
--- /dev/null
+++ b/mocks/mocks.go
@@ -0,0 +1,6 @@
+package mocks
+
+import _ "github.com/golang/mock/mockgen/model"
+
+//go:generate mockgen -package=mocks -destination=mock_worker.go github.com/golang-queue/queue/core Worker
+//go:generate mockgen -package=mocks -destination=mock_message.go github.com/golang-queue/queue/core QueuedMessage
diff --git a/options.go b/options.go
index f6e47c9..26b03b9 100644
--- a/options.go
+++ b/options.go
@@ -4,6 +4,8 @@ import (
 	"context"
 	"runtime"
 	"time"
+
+	"github.com/golang-queue/queue/core"
 )
 
 var (
@@ -11,7 +13,7 @@ var (
 	defaultWorkerCount = runtime.NumCPU()
 	defaultTimeout     = 60 * time.Minute
 	defaultNewLogger   = NewLogger()
-	defaultFn          = func(context.Context, QueuedMessage) error { return nil }
+	defaultFn          = func(context.Context, core.QueuedMessage) error { return nil }
 	defaultMetric      = NewMetric()
 )
 
@@ -47,14 +49,14 @@ func WithMetric(m Metric) Option {
 }
 
 // WithWorker set custom worker
-func WithWorker(w Worker) Option {
+func WithWorker(w core.Worker) Option {
 	return func(q *Options) {
 		q.worker = w
 	}
 }
 
 // WithFn set custom job function
-func WithFn(fn func(context.Context, QueuedMessage) error) Option {
+func WithFn(fn func(context.Context, core.QueuedMessage) error) Option {
 	return func(q *Options) {
 		q.fn = fn
 	}
@@ -73,8 +75,8 @@ type Options struct {
 	timeout     time.Duration
 	logger      Logger
 	queueSize   int
-	worker      Worker
-	fn          func(context.Context, QueuedMessage) error
+	worker      core.Worker
+	fn          func(context.Context, core.QueuedMessage) error
 	metric      Metric
 }
 
diff --git a/queue.go b/queue.go
index 6e96c8f..45ad1d1 100644
--- a/queue.go
+++ b/queue.go
@@ -7,6 +7,8 @@ import (
 	"sync"
 	"sync/atomic"
 	"time"
+
+	"github.com/golang-queue/queue/core"
 )
 
 // ErrQueueShutdown the queue is released and closed.
@@ -25,7 +27,7 @@ type (
 		routineGroup *routineGroup
 		quit         chan struct{}
 		ready        chan struct{}
-		worker       Worker
+		worker       core.Worker
 		stopOnce     sync.Once
 		timeout      time.Duration
 		stopFlag     int32
@@ -139,16 +141,16 @@ func (q *Queue) Wait() {
 }
 
 // Queue to queue all job
-func (q *Queue) Queue(job QueuedMessage) error {
+func (q *Queue) Queue(job core.QueuedMessage) error {
 	return q.handleQueue(q.timeout, job)
 }
 
 // QueueWithTimeout to queue all job with specified timeout.
-func (q *Queue) QueueWithTimeout(timeout time.Duration, job QueuedMessage) error {
+func (q *Queue) QueueWithTimeout(timeout time.Duration, job core.QueuedMessage) error {
 	return q.handleQueue(timeout, job)
 }
 
-func (q *Queue) handleQueue(timeout time.Duration, job QueuedMessage) error {
+func (q *Queue) handleQueue(timeout time.Duration, job core.QueuedMessage) error {
 	if atomic.LoadInt32(&q.stopFlag) == 1 {
 		return ErrQueueShutdown
 	}
@@ -200,7 +202,7 @@ func (q *Queue) handleQueueTask(timeout time.Duration, task TaskFunc) error {
 	return nil
 }
 
-func (q *Queue) work(task QueuedMessage) {
+func (q *Queue) work(task core.QueuedMessage) {
 	var err error
 	// to handle panic cases from inside the worker
 	// in such case, we start a new goroutine
@@ -246,7 +248,7 @@ func (q *Queue) schedule() {
 
 // start handle job
 func (q *Queue) start() {
-	tasks := make(chan QueuedMessage, 1)
+	tasks := make(chan core.QueuedMessage, 1)
 
 	for {
 		// request task from queue in background
diff --git a/queue_test.go b/queue_test.go
index 98d5a2e..e78c57c 100644
--- a/queue_test.go
+++ b/queue_test.go
@@ -4,6 +4,8 @@ import (
 	"testing"
 	"time"
 
+	"github.com/golang-queue/queue/core"
+
 	"github.com/stretchr/testify/assert"
 	"go.uber.org/goleak"
 )
@@ -40,7 +42,7 @@ func TestNewQueue(t *testing.T) {
 
 func TestShtdonwOnce(t *testing.T) {
 	w := &messageWorker{
-		messages: make(chan QueuedMessage, 100),
+		messages: make(chan core.QueuedMessage, 100),
 	}
 	q, err := NewQueue(
 		WithWorker(w),
@@ -60,7 +62,7 @@ func TestShtdonwOnce(t *testing.T) {
 
 func TestCapacityReached(t *testing.T) {
 	w := &messageWorker{
-		messages: make(chan QueuedMessage, 1),
+		messages: make(chan core.QueuedMessage, 1),
 	}
 	q, err := NewQueue(
 		WithWorker(w),
@@ -81,7 +83,7 @@ func TestCapacityReached(t *testing.T) {
 
 func TestCloseQueueAfterShutdown(t *testing.T) {
 	w := &messageWorker{
-		messages: make(chan QueuedMessage, 10),
+		messages: make(chan core.QueuedMessage, 10),
 	}
 	q, err := NewQueue(
 		WithWorker(w),
diff --git a/worker_empty.go b/worker_empty.go
index 578a2ce..2486bb1 100644
--- a/worker_empty.go
+++ b/worker_empty.go
@@ -1,11 +1,13 @@
 package queue
 
-var _ Worker = (*emptyWorker)(nil)
+import "github.com/golang-queue/queue/core"
+
+var _ core.Worker = (*emptyWorker)(nil)
 
 // just for unit testing, don't use it.
 type emptyWorker struct{}
 
-func (w *emptyWorker) Run(task QueuedMessage) error    { return nil }
-func (w *emptyWorker) Shutdown() error                 { return nil }
-func (w *emptyWorker) Queue(task QueuedMessage) error  { return nil }
-func (w *emptyWorker) Request() (QueuedMessage, error) { return nil, nil }
+func (w *emptyWorker) Run(task core.QueuedMessage) error    { return nil }
+func (w *emptyWorker) Shutdown() error                      { return nil }
+func (w *emptyWorker) Queue(task core.QueuedMessage) error  { return nil }
+func (w *emptyWorker) Request() (core.QueuedMessage, error) { return nil, nil }
diff --git a/worker_message.go b/worker_message.go
index de99730..277fdba 100644
--- a/worker_message.go
+++ b/worker_message.go
@@ -3,16 +3,18 @@ package queue
 import (
 	"errors"
 	"time"
+
+	"github.com/golang-queue/queue/core"
 )
 
-var _ Worker = (*messageWorker)(nil)
+var _ core.Worker = (*messageWorker)(nil)
 
 // just for unit testing, don't use it.
 type messageWorker struct {
-	messages chan QueuedMessage
+	messages chan core.QueuedMessage
 }
 
-func (w *messageWorker) Run(task QueuedMessage) error {
+func (w *messageWorker) Run(task core.QueuedMessage) error {
 	if string(task.Bytes()) == "panic" {
 		panic("show panic")
 	}
@@ -25,7 +27,7 @@ func (w *messageWorker) Shutdown() error {
 	return nil
 }
 
-func (w *messageWorker) Queue(task QueuedMessage) error {
+func (w *messageWorker) Queue(task core.QueuedMessage) error {
 	select {
 	case w.messages <- task:
 		return nil
@@ -34,7 +36,7 @@ func (w *messageWorker) Queue(task QueuedMessage) error {
 	}
 }
 
-func (w *messageWorker) Request() (QueuedMessage, error) {
+func (w *messageWorker) Request() (core.QueuedMessage, error) {
 	select {
 	case task := <-w.messages:
 		return task, nil
diff --git a/worker_task.go b/worker_task.go
index a3f1d0a..0edf79e 100644
--- a/worker_task.go
+++ b/worker_task.go
@@ -3,16 +3,18 @@ package queue
 import (
 	"context"
 	"errors"
+
+	"github.com/golang-queue/queue/core"
 )
 
-var _ Worker = (*taskWorker)(nil)
+var _ core.Worker = (*taskWorker)(nil)
 
 // just for unit testing, don't use it.
 type taskWorker struct {
-	messages chan QueuedMessage
+	messages chan core.QueuedMessage
 }
 
-func (w *taskWorker) Run(task QueuedMessage) error {
+func (w *taskWorker) Run(task core.QueuedMessage) error {
 	if v, ok := task.(Job); ok {
 		if v.Task != nil {
 			_ = v.Task(context.Background())
@@ -26,7 +28,7 @@ func (w *taskWorker) Shutdown() error {
 	return nil
 }
 
-func (w *taskWorker) Queue(job QueuedMessage) error {
+func (w *taskWorker) Queue(job core.QueuedMessage) error {
 	select {
 	case w.messages <- job:
 		return nil
@@ -35,7 +37,7 @@ func (w *taskWorker) Queue(job QueuedMessage) error {
 	}
 }
 
-func (w *taskWorker) Request() (QueuedMessage, error) {
+func (w *taskWorker) Request() (core.QueuedMessage, error) {
 	select {
 	case task := <-w.messages:
 		return task, nil
diff --git a/worker_task_test.go b/worker_task_test.go
index 547a9ff..62280e5 100644
--- a/worker_task_test.go
+++ b/worker_task_test.go
@@ -5,12 +5,14 @@ import (
 	"testing"
 	"time"
 
+	"github.com/golang-queue/queue/core"
+
 	"github.com/stretchr/testify/assert"
 )
 
 func TestQueueTaskJob(t *testing.T) {
 	w := &taskWorker{
-		messages: make(chan QueuedMessage, 10),
+		messages: make(chan core.QueuedMessage, 10),
 	}
 	q, err := NewQueue(
 		WithWorker(w),
diff --git a/worker_test.go b/worker_test.go
new file mode 100644
index 0000000..47095bc
--- /dev/null
+++ b/worker_test.go
@@ -0,0 +1,34 @@
+package queue
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/golang-queue/queue/core"
+	"github.com/golang-queue/queue/mocks"
+
+	"github.com/golang/mock/gomock"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestMockWorkerAndMessage(t *testing.T) {
+	controller := gomock.NewController(t)
+	defer controller.Finish()
+
+	m := mocks.NewMockQueuedMessage(controller)
+
+	w := mocks.NewMockWorker(controller)
+	w.EXPECT().Shutdown().Return(nil)
+	w.EXPECT().Request().DoAndReturn(func() (core.QueuedMessage, error) {
+		return m, errors.New("nil")
+	})
+
+	q, err := NewQueue(
+		WithWorker(w),
+		WithWorkerCount(1),
+	)
+	assert.NoError(t, err)
+	assert.NotNil(t, q)
+	q.Start()
+	q.Release()
+}