Mockito vs JMockit, battle of the mocking frameworks

The art of pretending

In all it’s glory

• Has been around since 2008• Is the industry standard ever since • In 2013 more then 30.000 Github

project• More popular then Spring and

Guava

• Most distinguishing feature• Verify the behaviour of the SUT

without establishing expectations beforehand

Mockito in action

Mockito in action

Mockito in action

So for, so good

• Arrange, Act, Assert• Mock any class, interface, method• No need for introducing test

interface shims• Declarative style for setting up

behaviour• Declarative style for verifying

behaviour

• …• In the happy flow

This gun’ be good

This gonna be good

• Mocking void methods• Mocking finals• Mocking statics• Verifying constructors

This gonna be good

• Make a test shim• Extend the class and scoop the

methods• Make an adapter or facade• Why aren’t they using interfaces

in the first place• The final keyword should be

banned• Let’s agree not to test this• Ahh.. let’s use

PowerMockito!

JMockit

JMockit in action

JMockit in action

JMockit in action

JMockit in action

• Expectations are like Mockito.when(…)

• Verifications are like Mockito.verify(…)

JMockit in action

• Uniform notation for• Primitives• Complex objects• Exceptions• Custom Answers

JMockit in action

Annotations - With great power…

• @Injectable• Single mock instance

• @Mocked• Entire class mock (at bytecode level)

• @Capturing• Any derived instance and subclass will be a class

mock

• @Tested• System under test• Tries to satisfy Constructor, @Autowired,

@Injectable

… comes great responsibility - Scoping

Legacy mock injection

Real world examples

java.lang.RuntimeException: Method getWindow in android.app.Activity not mocked. See http://g.co/androidstudio/not-mocked for details.

at android.app.Activity.getWindow(Activity.java) at android.support.v7.app.AppCompatDelegate.create(AppCompatDelegate.java:117) at android.support.v7.app.AppCompatActivity.getDelegate(AppCompatActivity.java:456) at android.support.v7.app.AppCompatActivity.onCreate(AppCompatActivity.java:59) at ExampleActivity.onCreate(ExampleActivity.java:15) at ExampleActivityTest. shouldCommitFragment_whenOnCreateIsCalled(ExampleActivityTest.java:9)

Real world examplesakka.actor.ActorInitializationException: You cannot create an instance of [com.cc.LoggingHandler] explicitly using the constructor (new). You have to use one of the 'actorOf' factory methods to create a new actor. See the documentation.

at akka.actor.ActorInitializationException$.apply(Actor.scala:173)at akka.actor.Actor$class.$init$(Actor.scala:436)at akka.actor.UntypedActor.<init>(UntypedActor.scala:97)at com.cc.LoggingHandler.<init>(LoggingHandler.java:14)at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native

Method)at java.lang.reflect.Constructor.newInstance(Constructor.java:423)at …

Real world examples

JMockit

JMockit

JMockit’s Advantages

• Mockito’s distinguishing feature covered by JMockit• Verify the behaviour of the SUT without establishing

expectations beforehand

• No need for special test runners

• No limit on testing statics, finals, constructors and whatnot

• No limitations/anomalies in your code due to the test framework

JMockit’s Disadvantages

• Risk of introducing in your code• Static methods• Not using dependency injection

• Need to get accustomed to new mocking framework

• Mockito’s error messages are more explicit

• Mockito forces proper dependencies

Some figures

• Github grade and maven dependencies• Mockito: 131.525• JMockit: 3.058

• First mentioned - first release:• Mockito: 2008 - 2008• JMockit: 2006 - 2012

• Both under constant development

Read more

• Official pages:• Mockito: http://mockito.org/• JMockit: http://jmockit.org/

• My blog:• www.endran.nl/blog• Mockito vs JMockit, battle of the

mocking frameworks• Death to statics

“I Don’t Always Test My Code. But When I Do, I Do It In Production.”