diff --git a/playground/mocklib/mocks/Robot.go b/playground/mocklib/mocks/Robot.go
new file mode 100644
index 0000000..3b4833d
--- /dev/null
+++ b/playground/mocklib/mocks/Robot.go
@@ -0,0 +1,15 @@
+// Code generated by mockery v1.0.0. DO NOT EDIT.
+
+package mocks
+
+import mock "github.com/stretchr/testify/mock"
+
+// Robot is an autogenerated mock type for the Robot type
+type Robot struct {
+	mock.Mock
+}
+
+// SayHi provides a mock function with given fields:
+func (_m *Robot) SayHi() {
+	_m.Called()
+}
diff --git a/playground/mocklib/robot.go b/playground/mocklib/robot.go
new file mode 100644
index 0000000..b3e0cc1
--- /dev/null
+++ b/playground/mocklib/robot.go
@@ -0,0 +1,45 @@
+package mocklib
+
+import "fmt"
+
+// Robot
+type Robot interface {
+	SayHi()
+}
+
+// ServiceRobot is kind of Robot can offer services
+type ServiceRobot struct {
+}
+
+func (robot *ServiceRobot) SayHi() {
+	fmt.Println("Hi, I'm service robot")
+}
+
+// IndustrialRobot is kind of Robot can do some jobs
+type IndustrialRobot struct {
+}
+
+func (robot *IndustrialRobot) SayHi() {
+	fmt.Println("Hi, I'm industrial robot")
+}
+
+func StartRobots() {
+	robots := initializeRobots()
+	makeRobotsSayHi(robots)
+}
+
+// initialize all robots
+func initializeRobots() []Robot {
+	robots := []Robot{
+		&ServiceRobot{},
+		&IndustrialRobot{},
+	}
+	return robots
+}
+
+// makeRobotsSayHi is used for making robots say hi
+func makeRobotsSayHi(robots []Robot) {
+	for _, robot := range robots {
+		robot.SayHi()
+	}
+}
diff --git a/playground/mocklib/robot_test.go b/playground/mocklib/robot_test.go
new file mode 100644
index 0000000..d02385e
--- /dev/null
+++ b/playground/mocklib/robot_test.go
@@ -0,0 +1,32 @@
+package mocklib
+
+import (
+	"github.com/weichou1229/go-patterns/playground/mocklib/mocks"
+	"testing"
+)
+
+func TestStartRobots(t *testing.T) {
+	StartRobots()
+}
+
+func TestMakeRobotsSayHi(t *testing.T) {
+	// create an instance of our test object
+	mockRobotA := new(mocks.Robot)
+	mockRobotB := new(mocks.Robot)
+
+	// setup expectations
+	mockRobotA.On("SayHi").Return(nil, nil)
+	mockRobotB.On("SayHi").Return(nil, nil)
+
+	robots := []Robot{
+		mockRobotA,
+		mockRobotB,
+	}
+
+	// Act
+	makeRobotsSayHi(robots)
+
+	// Assert that the expectations were met
+	mockRobotA.AssertExpectations(t)
+	mockRobotB.AssertExpectations(t)
+}