Mocks introduction

● Classic style
● Mockist style
● Different tools
● Links
Contents

● State verification
● Heavyweight dependencies
● Test doubles (Dummy, Fake, Stub, Mock)
Unit to be tested
DatabaseE-mail system
Other objects
Classic Style

Example. Dog and House
package com.sperasoft.test;
public class Dog {
private House home;
public boolean isPleasured() {
if (home == null) {
return false;
}
return (home.getWidth() * home.getHeight() *
home.getDepth() > 3);
}
public void settleIn(House home) {
this.home = home;
}
}
public interface House {
int getWidth();
int getHeight();
int getDepth();
}
Dog Class House Interface

public class HouseImpl implements House {
private int w;
private int h;
private int d;
public HouseImpl(int width, int height, int depth) {
w = width;
h = height;
d = depth;
}
public int getWidth() {
return w;
}
public int getHeight() {
return h;
}
public int getDepth() {
return d;
}
}
House Implementation

import static org.junit.Assert.*;
import org.junit.Test;
public class DogTest {
@Test
public void testIsPleasuredWithBigHouse() {
Dog dog = new Dog();
House dogHouse = new HouseImpl(1, 2, 3);
dog.settleIn(dogHouse);
assertTrue(dog.isPleasured());
}
//other test methods
}
Classic Test

import static org.junit.Assert.*;
public class DogTest {
@Test
House dogHouse = new House() {
public int getWidth() {
return 1;
}
public int getHeight() {
return 2;
}
public int getDepth() {
return 3;
}
};
}
}
Classic Test with Stub

import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;
import mockit.Mocked;
import mockit.NonStrictExpectations;
public class DogTestJMockit {
@Mocked
private House houseMock;
@Test
new NonStrictExpectations() {
{
houseMock.getWidth(); result
= 1;
houseMock.getHeight(); result
= 2;
houseMock.getDepth(); result
= 3; maxTimes = 1;
}
};
dog.settleIn(houseMock);
}
}
Test with Mocks

Weather!
final public class Weather {
static public int getTemperature() {
return (int)(Math.random()*60 —
20);
}
}

public class Dog {
private House home;
public boolean isPleasured() {
if (home == null) {
return false;
}
if (Weather.getTemperature() > 30 || Weather.getTemperature() < 20)
{
return false;
}
return (home.getWidth() * home.getHeight() * home.getDepth() > 3);
}
public void settleIn(House home) {
this.home = home;
}
}
Dog & Weather

//...imports
import mockit.Mocked;
import mockit.NonStrictExpectations;
public class DogTestJMockit {
@Mocked
private House houseMock;
@Mocked
private Weather weatherMock;
@Test
new NonStrictExpectations() {
{
houseMock.getWidth(); result = 1;
houseMock.getHeight(); result = 2;
houseMock.getDepth(); result = 3; maxTimes = 1;
Weather.getTemperature(); result = 25; times = 1;
}
};
dog.settleIn(houseMock);
}
}
Mocking Weather

● Setup and verification are extended by expectations
● Behaviour verification
● Need Driven Development
● Test spies alternative (stubs with behaviour verifications)
Unit to be tested
MockMock
Mock
Mocks Style

Advantages of Mocks
● Immediate neighbours only
● Outside-in style
● Test isolation
● Good to test objects that don't change their state

● Additional knowledge
● Difficult to maintain
● Heavy coupling to an implementation
Have to use TDD. Tests first. Use loose expectations to avoid this.
● Overhead additional libraries settings
● Addictive
Disadvantages of Mocks

import org.easymock.EasyMock;
public class DogTestEasyMock {
@Test
House dogHouse = EasyMock.createMock(House.class);
EasyMock.expect(dogHouse.getWidth()).andReturn(1);
EasyMock.expect(dogHouse.getHeight()).andReturn(2);
EasyMock.expect(dogHouse.getDepth()).andReturn(3).times(0, 1);
EasyMock.replay(dogHouse);
}
}
EasyMock

import org.jmock.Expectations;
import org.jmock.Mockery;
public class DogTestJMock {
@Test
Mockery context = new Mockery();
Dog d = new Dog();
final House dogHouse = context.mock(House.class);
Expectations expectations = new Expectations() {
{
allowing(dogHouse).getWidth();
will(returnValue(1));
allowing(dogHouse).getHeight();
oneOf(dogHouse).getDepth();
}
};
context.checking(expectations);
d.settleIn(dogHouse);
assertTrue(d.isPleasured());
}
}
JMock

import org.mockito.Mockito;
public class DogTestMockito {
@Test
House dogHouse = Mockito.mock(House.class);
Mockito.when(dogHouse.getWidth()).thenReturn(1);
Mockito.when(dogHouse.getHeight()).thenReturn(2);
Mockito.when(dogHouse.getDepth()).thenReturn(3);
Mockito.verify(dogHouse, Mockito.times(1)).getDepth();
}
}
Mockito

● M. Fowler «Mocks aren't stubs»
http://martinfowler.com/articles/mocksArentStubs.html
● Gerard Meszaros's book «Xunit test patterns»
http://xunitpatterns.com/
● Dan North's Behaviour Driven Development
http://dannorth.net/introducing-bdd/
● Jmock. http://www.jmock.org/
● EasyMock http://easymock.org/
● Mockito http://code.google.com/p/mockito/
● Jmockit http://code.google.com/p/jmockit/
Links

Mocks introduction

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