Learning art of Mocking by EasyMock

Deepak Singhvi

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Agenda

Goal Unit Testing… can be easy or hard What’s a Mock? Using Mock Objects Mock Frameworks To Mock or not to EasyMock Overview, Features, Drawbacks EasyMock in details – by examples Conclusion

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Goal of Presentation

Show how “Mocking Objects” can greatly improve unit testing by facilitating tests that are easier to write and less dependant upon objects outside the test domain

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UT is easy when…

Unit testing is easy when

– your code does not depend on any thing No database, file system, web service, socket, …

dependencies

– your code can be tested fully in isolation

–Does not require other classes/components, frameworks, etc.

You quickly create an object, run some tests, and off you go

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But remember UT means Automation

But when we talk about unit testing, we mean automated unit testing.

We need to be able to run tests quickly. Run them as many times as we like. You certainly don’t want to do either

laborious and/or manual setup and teardown. You want to check for behavior and ill

behavior of dependent code as well.

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testing is easy in isolation

Class Under Test

Test Class

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testing is harder with dependencies …

Class Under Test

Test Class

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… so remove the dependencies (for developer testing)

Class Under Test

Test Class

mock

mock

mockm

ock

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Topics of Discussion

What is Object Mocking? Why Mock Objects? What tools are available to support Object

Mockery

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What is Object Mocking?

Mock objects simulate (fake) real objects Allows for more modular testing Creating a mock implementation of an object that

can be used as a stand-in in testing Records and verifies expectations of calls A mock objects allow you to set expectations The mock object lets you verify that the expectations

were met or not Use the same Interface(s) as the real object

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Why engage in Object Mocking?

The real object has behavior that is hard to cause or is non-deterministic.

The real object is difficult to set up. The real object is slow. The real object has (or is ) a UI. Test needs to query the object but queries are not available. Real objects do not exist ( Team A is working on X and required Y.y

from Team B, at the same time team B is working on Y, to start the task of X team A can mock Y.y)

Can simulate both behavior and ill-behavior ( For e.g. there is a particular ill behavior which can appear only in the field, but we work on simulation and its difficult to get ill-behavior)

speeds up development of code under test

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To Mock or not to?

To– Mock only code that code under test directly depends on– Mock object that is hard to work with– Mock object that takes effort to set up– Mock object whose behavior is hard to predict– Mock object that requires lots of resources– Mock objects that are computationally expensive or very slow to respond– Mock objects that your test needs to verify with

Not To– Do not mock for the sake of mocking, ask if you can eliminate the need for mock by refactoring your code– Mock your objects but not resources like database, etc.– When writing the real code is easier than writing mock– Do not mock what will slow down your UT, mocks should be used to speed up UT

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What tools are available to support Obect Mockery

The MockObjects framework MockMaker JMock NMock EasyMock (We are interested only in this

particular tool)

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EasyMock Overview

Open source tool available at easymock.org Uses reflection to dynamically create proxies

that implement the interface at run time EasyMock generates two objects the

EasyMock Mock Object and the EasyMock Mock Control

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EasyMock Features

Allows the expected parameter value to be set for each method

Allows you to set up the value to be returned by each method

Allows the number of times the method is to be invoked to be specified

Allows you to specify an exception the a method should throw

Will verify that everything went as expected

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EasyMock Drawbacks

EasyMock generates objects on the fly so you can’t add any behaviour

EasyMock uses the equals method to compare parameters

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General

Homepage: www.easymock.org Lizence: MIT-Lizence

– Open Source– Very liberal

1. Version: 2003 Latest Version: April 2006

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Installation

Download easymock2.2.zip Add easymock.jar as library Used in Unit-test (JUnit/TestNG)

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EasyMock in detail

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How to use it

To get a Mock Object, we need to 1) Create a Mock Object for the interface we would like to simulate, 2) Record the expected behavior, 3) And switch the Mock Object to replay state.

EasyMock uses a record/replay metaphor for setting expectations. For each object you wish to mock you create a mock object. To indicate an expectation you call the method, with the arguments you expect on the mock. Once you've finished setting expectations you call replay - at which point the mock finishes the recording and is ready to respond to the primary object. Once done you call verify.

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Creating A Mock

IEnumeration<Short> iEnumIntfMock =

EasyMock.createMock(EnumeratedAttribute.class);

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Expecting A Lot

Expect method is called on mock Expect sequence of method calls on mock

(call createStrictMock()) Expect parameters to methods calls on mock

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Expect A Call

EasyMock.expect(iEnumIntfMock.getNumberOfRows());

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Expect A Return

EasyMock.expect(iEnumIntfMock.getNumberOfRows()).andReturn(5);

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Replay

Prime the pump to walk through expected call sequence

Provide return values in same sequence Listen to usage of call parameters

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Replay Kickoff

EasyMock.replay(iEnumIntfMock);

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Call all functions as you normally would Pass in mock where injectable Consider how mock can be passed into

internal references

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Testing

int numOfRows =

iEnumIntfMock.getNumberOfRows();

Assert.assertTrue("Number of rows does not match", numOfRows > 0);

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Verifying

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Called after all operations with the mock are done

Compares the usage to the recording

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Verifying

EasyMock.verify(iEnumIntfMock);

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Nice Mocks

Mocks created by EasyMock usually throw an AssertionError for all unexpected method calls. Sometimes you need a mock that nicely returns default values instead of complaining all the time. Mocks created by EasyMock.createNiceMock() return empty values (0, null, or false) for unexpected method calls.

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Strict Mocks

By default, the order of method calls is not checked by EasyMock. If you need this, you have to create a Strict Mock with EasyMock.createStrictMock(). You can even switch from strict to normal by EasyMock.checkOrder(Object mock, boolean enableOrderCheck).

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What about Mocking Classes with EasyMock?

So far we've used EasyMock to create mocks for interfaces, but how about mocking classes?

Is that possible? No. Yes. No. Yes, well, EasyMock itself is capable of mocking interfaces only.

But there is another project called EasyMock Class Extension that fills this gap. Just use the org.easymock.classextension.EasyMock.* methods instead. You

may even mock abstract classes. Unfortunately (but not surprisingly), you can't mock final classes.

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What this means

Object Mocking is an invaluable technique for improving the overall quality of your unit tests.

Help keep design decoupled Check code’s usage of another

object Test code from the inside out Make tests run faster Make it easier to write code for

problematic resources Defer having to write a class

Test components in isolation from the rest of the system

Promote interface-based design

Encourage composition over inheritance

Refine interfaces Test unusual, unlikely, and

exceptional situations

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Quiz Time

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Mocking is one of the most popular tool used Agile and Extreme programming methodologies to follow the Test Driven Development

( popularly known as TDD).

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Thank You

deepak.singhvi@gmail.com